diff --git a/gfx/2d/Rect.h b/gfx/2d/Rect.h
index db0f45d373b67..c102e501b6168 100644
--- a/gfx/2d/Rect.h
+++ b/gfx/2d/Rect.h
@@ -99,6 +99,12 @@ struct IntRectTyped :
       yMost += this->height;
       return !xMost.isValid() || !yMost.isValid();
     }
+
+    // This is here only to keep IPDL-generated code happy. DO NOT USE.
+    bool operator==(const IntRectTyped<units>& aRect) const
+    {
+      return IntRectTyped<units>::IsEqualEdges(aRect);
+    }
 };
 typedef IntRectTyped<UnknownUnits> IntRect;
 
diff --git a/gfx/layers/LayerMetricsWrapper.h b/gfx/layers/LayerMetricsWrapper.h
index e92e2fcd382a3..19d8e82124ffa 100644
--- a/gfx/layers/LayerMetricsWrapper.h
+++ b/gfx/layers/LayerMetricsWrapper.h
@@ -341,15 +341,17 @@ class MOZ_STACK_CLASS LayerMetricsWrapper {
     return region;
   }
 
-  const nsIntRect* GetClipRect() const
+  const Maybe<ParentLayerIntRect>& GetClipRect() const
   {
     MOZ_ASSERT(IsValid());
 
+    static const Maybe<ParentLayerIntRect> sNoClipRect = Nothing();
+
     if (AtBottomLayer()) {
       return mLayer->GetClipRect();
     }
 
-    return nullptr;
+    return sNoClipRect;
   }
 
   EventRegionsOverride GetEventRegionsOverride() const
diff --git a/gfx/layers/LayerTreeInvalidation.cpp b/gfx/layers/LayerTreeInvalidation.cpp
index 836f8661f1be3..56a8f08bf070d 100644
--- a/gfx/layers/LayerTreeInvalidation.cpp
+++ b/gfx/layers/LayerTreeInvalidation.cpp
@@ -8,6 +8,7 @@
 #include "ImageContainer.h"             // for ImageContainer
 #include "ImageLayers.h"                // for ImageLayer, etc
 #include "Layers.h"                     // for Layer, ContainerLayer, etc
+#include "Units.h"                      // for ParentLayerIntRect
 #include "gfxColor.h"                   // for gfxRGBA
 #include "GraphicsFilter.h"             // for GraphicsFilter
 #include "gfxRect.h"                    // for gfxRect
@@ -140,7 +141,7 @@ struct LayerPropertiesBase : public LayerProperties
                             mLayer->GetPostXScale() != mPostXScale ||
                             mLayer->GetPostYScale() != mPostYScale;
     Layer* otherMask = mLayer->GetMaskLayer();
-    const nsIntRect* otherClip = mLayer->GetClipRect();
+    const Maybe<ParentLayerIntRect>& otherClip = mLayer->GetClipRect();
     nsIntRegion result;
     if ((mMaskLayer ? mMaskLayer->mLayer : nullptr) != otherMask ||
         (mUseClipRect != !!otherClip) ||
@@ -166,7 +167,7 @@ struct LayerPropertiesBase : public LayerProperties
       if (!mClipRect.IsEqualInterior(*otherClip)) {
         aGeometryChanged = true;
         nsIntRegion tmp; 
-        tmp.Xor(mClipRect, *otherClip); 
+        tmp.Xor(ParentLayerIntRect::ToUntyped(mClipRect), ParentLayerIntRect::ToUntyped(*otherClip)); 
         AddRegion(result, tmp);
       }
     }
@@ -199,7 +200,7 @@ struct LayerPropertiesBase : public LayerProperties
   float mPostXScale;
   float mPostYScale;
   float mOpacity;
-  nsIntRect mClipRect;
+  ParentLayerIntRect mClipRect;
   bool mUseClipRect;
 };
 
diff --git a/gfx/layers/Layers.cpp b/gfx/layers/Layers.cpp
index 94f642439e02b..2488ca18ae8bd 100644
--- a/gfx/layers/Layers.cpp
+++ b/gfx/layers/Layers.cpp
@@ -14,6 +14,7 @@
 #include "LayerSorter.h"                // for SortLayersBy3DZOrder
 #include "LayersLogging.h"              // for AppendToString
 #include "ReadbackLayer.h"              // for ReadbackLayer
+#include "UnitTransforms.h"             // for ViewAs
 #include "gfxPlatform.h"                // for gfxPlatform
 #include "gfxPrefs.h"
 #include "gfxUtils.h"                   // for gfxUtils, etc
@@ -201,7 +202,6 @@ Layer::Layer(LayerManager* aManager, void* aImplData) :
   mMixBlendMode(CompositionOp::OP_OVER),
   mForceIsolatedGroup(false),
   mContentFlags(0),
-  mUseClipRect(false),
   mUseTileSourceRect(false),
   mIsFixedPosition(false),
   mMargins(0, 0, 0, 0),
@@ -547,7 +547,7 @@ Layer::CanUseOpaqueSurface()
 
 // NB: eventually these methods will be defined unconditionally, and
 // can be moved into Layers.h
-const nsIntRect*
+const Maybe<ParentLayerIntRect>&
 Layer::GetEffectiveClipRect()
 {
   if (LayerComposite* shadow = AsLayerComposite()) {
@@ -673,7 +673,9 @@ Layer::CalculateScissorRect(const RenderTargetIntRect& aCurrentScissorRect)
     return currentClip;
   }
 
-  const RenderTargetIntRect clipRect = RenderTargetPixel::FromUntyped(*GetEffectiveClipRect());
+  const RenderTargetIntRect clipRect =
+    ViewAs<RenderTargetPixel>(*GetEffectiveClipRect(),
+                              PixelCastJustification::RenderTargetIsParentLayerForRoot);
   if (clipRect.IsEmpty()) {
     // We might have a non-translation transform in the container so we can't
     // use the code path below.
@@ -694,7 +696,7 @@ Layer::CalculateScissorRect(const RenderTargetIntRect& aCurrentScissorRect)
     if (!gfxUtils::GfxRectToIntRect(trScissor, &tmp)) {
       return RenderTargetIntRect(currentClip.TopLeft(), RenderTargetIntSize(0, 0));
     }
-    scissor = RenderTargetPixel::FromUntyped(tmp);
+    scissor = ViewAs<RenderTargetPixel>(tmp);
 
     // Find the nearest ancestor with an intermediate surface
     do {
@@ -884,7 +886,7 @@ Layer::GetVisibleRegionRelativeToRootLayer(nsIntRegion& aResult,
     // If the parent layer clips its lower layers, clip the visible region
     // we're accumulating.
     if (layer->GetEffectiveClipRect()) {
-      aResult.AndWith(*layer->GetEffectiveClipRect());
+      aResult.AndWith(ParentLayerIntRect::ToUntyped(*layer->GetEffectiveClipRect()));
     }
 
     // Now we need to walk across the list of siblings for this parent layer,
@@ -1099,7 +1101,7 @@ ContainerLayer::HasMultipleChildren()
 {
   uint32_t count = 0;
   for (Layer* child = GetFirstChild(); child; child = child->GetNextSibling()) {
-    const nsIntRect *clipRect = child->GetEffectiveClipRect();
+    const Maybe<ParentLayerIntRect>& clipRect = child->GetEffectiveClipRect();
     if (clipRect && clipRect->IsEmpty())
       continue;
     if (child->GetVisibleRegion().IsEmpty())
@@ -1166,7 +1168,7 @@ ContainerLayer::DefaultComputeEffectiveTransforms(const Matrix4x4& aTransformToS
         gfx::ThebesMatrix(contTransform).HasNonIntegerTranslation()) {
 #endif
         for (Layer* child = GetFirstChild(); child; child = child->GetNextSibling()) {
-          const nsIntRect *clipRect = child->GetEffectiveClipRect();
+          const Maybe<ParentLayerIntRect>& clipRect = child->GetEffectiveClipRect();
           /* We can't (easily) forward our transform to children with a non-empty clip
            * rect since it would need to be adjusted for the transform. See
            * the calculations performed by CalculateScissorRect above.
@@ -1565,8 +1567,8 @@ Layer::PrintInfo(std::stringstream& aStream, const char* aPrefix)
 
   layers::PrintInfo(aStream, AsLayerComposite());
 
-  if (mUseClipRect) {
-    AppendToString(aStream, mClipRect, " [clip=", "]");
+  if (mClipRect) {
+    AppendToString(aStream, *mClipRect, " [clip=", "]");
   }
   if (1.0 != mPostXScale || 1.0 != mPostYScale) {
     aStream << nsPrintfCString(" [postScale=%g, %g]", mPostXScale, mPostYScale).get();
@@ -1650,8 +1652,10 @@ DumpTransform(layerscope::LayersPacket::Layer::Matrix* aLayerMatrix, const Matri
 }
 
 // The static helper function sets the nsIntRect into the packet
+template <typename T, typename Sub, typename Point, typename SizeT, typename MarginT>
 static void
-DumpRect(layerscope::LayersPacket::Layer::Rect* aLayerRect, const nsIntRect& aRect)
+DumpRect(layerscope::LayersPacket::Layer::Rect* aLayerRect,
+         const BaseRect<T, Sub, Point, SizeT, MarginT>& aRect)
 {
   aLayerRect->set_x(aRect.x);
   aLayerRect->set_y(aRect.y);
@@ -1682,7 +1686,7 @@ Layer::DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent)
   // Shadow
   if (LayerComposite* lc = AsLayerComposite()) {
     LayersPacket::Layer::Shadow* s = layer->mutable_shadow();
-    if (const nsIntRect* clipRect = lc->GetShadowClipRect()) {
+    if (const Maybe<ParentLayerIntRect>& clipRect = lc->GetShadowClipRect()) {
       DumpRect(s->mutable_clip(), *clipRect);
     }
     if (!lc->GetShadowTransform().IsIdentity()) {
@@ -1693,8 +1697,8 @@ Layer::DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent)
     }
   }
   // Clip
-  if (mUseClipRect) {
-    DumpRect(layer->mutable_clip(), mClipRect);
+  if (mClipRect) {
+    DumpRect(layer->mutable_clip(), *mClipRect);
   }
   // Transform
   if (!mTransform.IsIdentity()) {
@@ -2047,7 +2051,7 @@ PrintInfo(std::stringstream& aStream, LayerComposite* aLayerComposite)
   if (!aLayerComposite) {
     return;
   }
-  if (const nsIntRect* clipRect = aLayerComposite->GetShadowClipRect()) {
+  if (const Maybe<ParentLayerIntRect>& clipRect = aLayerComposite->GetShadowClipRect()) {
     AppendToString(aStream, *clipRect, " [shadow-clip=", "]");
   }
   if (!aLayerComposite->GetShadowTransform().IsIdentity()) {
diff --git a/gfx/layers/Layers.h b/gfx/layers/Layers.h
index aef6f01248732..962c7bcc4cc22 100644
--- a/gfx/layers/Layers.h
+++ b/gfx/layers/Layers.h
@@ -10,7 +10,7 @@
 #include <stdio.h>                      // for FILE
 #include <sys/types.h>                  // for int32_t, int64_t
 #include "FrameMetrics.h"               // for FrameMetrics
-#include "Units.h"                      // for LayerMargin, LayerPoint
+#include "Units.h"                      // for LayerMargin, LayerPoint, ParentLayerIntRect
 #include "gfxContext.h"                 // for GraphicsOperator
 #include "gfxTypes.h"
 #include "gfxColor.h"                   // for gfxRGBA
@@ -21,6 +21,7 @@
 #include "mozilla/Assertions.h"         // for MOZ_ASSERT_HELPER2, etc
 #include "mozilla/DebugOnly.h"          // for DebugOnly
 #include "mozilla/EventForwards.h"      // for nsPaintEvent
+#include "mozilla/Maybe.h"              // for Maybe
 #include "mozilla/RefPtr.h"             // for TemporaryRef
 #include "mozilla/StyleAnimationValue.h" // for StyleAnimationValue, etc
 #include "mozilla/TimeStamp.h"          // for TimeStamp, TimeDuration
@@ -990,20 +991,20 @@ class Layer {
    * in device pixels.
    * If aRect is null no clipping will be performed.
    */
-  void SetClipRect(const nsIntRect* aRect)
+  void SetClipRect(const Maybe<ParentLayerIntRect>& aRect)
   {
-    if (mUseClipRect) {
+    if (mClipRect) {
       if (!aRect) {
         MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was %d,%d,%d,%d is <none>", this,
-                         mClipRect.x, mClipRect.y, mClipRect.width, mClipRect.height));
-        mUseClipRect = false;
+                         mClipRect->x, mClipRect->y, mClipRect->width, mClipRect->height));
+        mClipRect.reset();
         Mutated();
       } else {
-        if (!aRect->IsEqualEdges(mClipRect)) {
+        if (!aRect->IsEqualEdges(*mClipRect)) {
           MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was %d,%d,%d,%d is %d,%d,%d,%d", this,
-                           mClipRect.x, mClipRect.y, mClipRect.width, mClipRect.height,
+                           mClipRect->x, mClipRect->y, mClipRect->width, mClipRect->height,
                            aRect->x, aRect->y, aRect->width, aRect->height));
-          mClipRect = *aRect;
+          mClipRect = aRect;
           Mutated();
         }
       }
@@ -1011,8 +1012,7 @@ class Layer {
       if (aRect) {
         MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was <none> is %d,%d,%d,%d", this,
                          aRect->x, aRect->y, aRect->width, aRect->height));
-        mUseClipRect = true;
-        mClipRect = *aRect;
+        mClipRect = aRect;
         Mutated();
       }
     }
@@ -1227,7 +1227,7 @@ class Layer {
   // These getters can be used anytime.
   float GetOpacity() { return mOpacity; }
   gfx::CompositionOp GetMixBlendMode() const { return mMixBlendMode; }
-  const nsIntRect* GetClipRect() { return mUseClipRect ? &mClipRect : nullptr; }
+  const Maybe<ParentLayerIntRect>& GetClipRect() const { return mClipRect; }
   uint32_t GetContentFlags() { return mContentFlags; }
   const nsIntRect& GetLayerBounds() const { return mLayerBounds; }
   const nsIntRegion& GetVisibleRegion() const { return mVisibleRegion; }
@@ -1418,7 +1418,7 @@ class Layer {
   // These getters can be used anytime.  They return the effective
   // values that should be used when drawing this layer to screen,
   // accounting for this layer possibly being a shadow.
-  const nsIntRect* GetEffectiveClipRect();
+  const Maybe<ParentLayerIntRect>& GetEffectiveClipRect();
   const nsIntRegion& GetEffectiveVisibleRegion();
 
   /**
@@ -1700,12 +1700,11 @@ class Layer {
   float mOpacity;
   gfx::CompositionOp mMixBlendMode;
   bool mForceIsolatedGroup;
-  nsIntRect mClipRect;
+  Maybe<ParentLayerIntRect> mClipRect;
   nsIntRect mTileSourceRect;
   nsIntRegion mInvalidRegion;
   nsTArray<nsRefPtr<AsyncPanZoomController> > mApzcs;
   uint32_t mContentFlags;
-  bool mUseClipRect;
   bool mUseTileSourceRect;
   bool mIsFixedPosition;
   LayerPoint mAnchor;
diff --git a/gfx/layers/ReadbackProcessor.cpp b/gfx/layers/ReadbackProcessor.cpp
index b478ffb2c37c0..d0b40c4edc51b 100644
--- a/gfx/layers/ReadbackProcessor.cpp
+++ b/gfx/layers/ReadbackProcessor.cpp
@@ -7,6 +7,8 @@
 #include <sys/types.h>                  // for int32_t
 #include "Layers.h"                     // for Layer, PaintedLayer, etc
 #include "ReadbackLayer.h"              // for ReadbackLayer, ReadbackSink
+#include "UnitTransforms.h"             // for ViewAs
+#include "Units.h"                      // for ParentLayerIntRect
 #include "gfxColor.h"                   // for gfxRGBA
 #include "gfxContext.h"                 // for gfxContext
 #include "gfxUtils.h"
@@ -76,8 +78,8 @@ FindBackgroundLayer(ReadbackLayer* aLayer, nsIntPoint* aOffset)
       return nullptr;
 
     // cliprects are post-transform
-    const nsIntRect* clipRect = l->GetEffectiveClipRect();
-    if (clipRect && !clipRect->Contains(nsIntRect(transformOffset, aLayer->GetSize())))
+    const Maybe<ParentLayerIntRect>& clipRect = l->GetEffectiveClipRect();
+    if (clipRect && !clipRect->Contains(ViewAs<ParentLayerPixel>(nsIntRect(transformOffset, aLayer->GetSize()))))
       return nullptr;
 
     Layer::LayerType type = l->GetType();
diff --git a/gfx/layers/apz/src/APZCTreeManager.cpp b/gfx/layers/apz/src/APZCTreeManager.cpp
index f552db5c30795..e9cf259e233a7 100644
--- a/gfx/layers/apz/src/APZCTreeManager.cpp
+++ b/gfx/layers/apz/src/APZCTreeManager.cpp
@@ -29,6 +29,7 @@
 #include "gfxPrefs.h"                   // for gfxPrefs
 #include "OverscrollHandoffState.h"     // for OverscrollHandoffState
 #include "LayersLogging.h"              // for Stringify
+#include "Units.h"                      // for ParentlayerPixel
 
 #define ENABLE_APZCTM_LOGGING 0
 // #define ENABLE_APZCTM_LOGGING 1
@@ -202,7 +203,7 @@ ComputeClipRegion(GeckoContentController* aController,
 {
   ParentLayerIntRegion clipRegion;
   if (aLayer.GetClipRect()) {
-    clipRegion = ViewAs<ParentLayerPixel>(*aLayer.GetClipRect());
+    clipRegion = *aLayer.GetClipRect();
   } else {
     // if there is no clip on this layer (which should only happen for the
     // root scrollable layer in a process, or for some of the LayerMetrics
@@ -334,7 +335,7 @@ APZCTreeManager::PrepareNodeForLayer(const LayerMetricsWrapper& aLayer,
     node = RecycleOrCreateNode(aState, nullptr);
     AttachNodeToTree(node, aParent, aNextSibling);
     node->SetHitTestData(GetEventRegions(aLayer), aLayer.GetTransform(),
-        aLayer.GetClipRect() ? Some(ParentLayerIntRegion(ViewAs<ParentLayerPixel>(*aLayer.GetClipRect()))) : Nothing(),
+        aLayer.GetClipRect() ? Some(ParentLayerIntRegion(*aLayer.GetClipRect())) : Nothing(),
         GetEventRegionsOverride(aParent, aLayer));
     return node;
   }
diff --git a/gfx/layers/basic/BasicContainerLayer.cpp b/gfx/layers/basic/BasicContainerLayer.cpp
index 409bd6cb36b8e..116aaa3e37af2 100644
--- a/gfx/layers/basic/BasicContainerLayer.cpp
+++ b/gfx/layers/basic/BasicContainerLayer.cpp
@@ -102,7 +102,7 @@ BasicContainerLayer::ChildrenPartitionVisibleRegion(const nsIntRect& aInRect)
     childRegion.MoveBy(int32_t(childTransform._31), int32_t(childTransform._32));
     childRegion.And(childRegion, rect);
     if (l->GetClipRect()) {
-      childRegion.And(childRegion, *l->GetClipRect() + offset);
+      childRegion.And(childRegion, ParentLayerIntRect::ToUntyped(*l->GetClipRect()) + offset);
     }
     nsIntRegion intersection;
     intersection.And(covered, childRegion);
diff --git a/gfx/layers/basic/BasicLayerManager.cpp b/gfx/layers/basic/BasicLayerManager.cpp
index bc38a2f2cb8b5..b9f4caa54bd23 100644
--- a/gfx/layers/basic/BasicLayerManager.cpp
+++ b/gfx/layers/basic/BasicLayerManager.cpp
@@ -324,9 +324,9 @@ MarkLayersHidden(Layer* aLayer, const nsIntRect& aClipRect,
   }
 
   {
-    const nsIntRect* clipRect = aLayer->GetEffectiveClipRect();
+    const Maybe<ParentLayerIntRect>& clipRect = aLayer->GetEffectiveClipRect();
     if (clipRect) {
-      nsIntRect cr = *clipRect;
+      nsIntRect cr = ParentLayerIntRect::ToUntyped(*clipRect);
       // clipRect is in the container's coordinate system. Get it into the
       // global coordinate system.
       if (aLayer->GetParent()) {
@@ -404,9 +404,9 @@ ApplyDoubleBuffering(Layer* aLayer, const nsIntRect& aVisibleRect)
   nsIntRect newVisibleRect(aVisibleRect);
 
   {
-    const nsIntRect* clipRect = aLayer->GetEffectiveClipRect();
+    const Maybe<ParentLayerIntRect>& clipRect = aLayer->GetEffectiveClipRect();
     if (clipRect) {
-      nsIntRect cr = *clipRect;
+      nsIntRect cr = ParentLayerIntRect::ToUntyped(*clipRect);
       // clipRect is in the container's coordinate system. Get it into the
       // global coordinate system.
       if (aLayer->GetParent()) {
@@ -865,7 +865,7 @@ BasicLayerManager::PaintLayer(gfxContext* aTarget,
 
   RenderTraceScope trace("BasicLayerManager::PaintLayer", "707070");
 
-  const nsIntRect* clipRect = aLayer->GetEffectiveClipRect();
+  const Maybe<ParentLayerIntRect>& clipRect = aLayer->GetEffectiveClipRect();
   BasicContainerLayer* container =
     static_cast<BasicContainerLayer*>(aLayer->AsContainerLayer());
   bool needsGroup = container && container->UseIntermediateSurface();
diff --git a/gfx/layers/composite/AsyncCompositionManager.cpp b/gfx/layers/composite/AsyncCompositionManager.cpp
index 71646a7b2a367..571e475b43d03 100644
--- a/gfx/layers/composite/AsyncCompositionManager.cpp
+++ b/gfx/layers/composite/AsyncCompositionManager.cpp
@@ -140,12 +140,10 @@ static void
 TransformClipRect(Layer* aLayer,
                   const Matrix4x4& aTransform)
 {
-  const nsIntRect* clipRect = aLayer->AsLayerComposite()->GetShadowClipRect();
+  const Maybe<ParentLayerIntRect>& clipRect = aLayer->AsLayerComposite()->GetShadowClipRect();
   if (clipRect) {
-    LayerIntRect transformed = TransformTo<LayerPixel>(
-        aTransform, LayerIntRect::FromUntyped(*clipRect));
-    nsIntRect shadowClip = LayerIntRect::ToUntyped(transformed);
-    aLayer->AsLayerComposite()->SetShadowClipRect(&shadowClip);
+    ParentLayerIntRect transformed = TransformTo<ParentLayerPixel>(aTransform, *clipRect);
+    aLayer->AsLayerComposite()->SetShadowClipRect(Some(transformed));
   }
 }
 
@@ -565,8 +563,8 @@ AdjustForClip(const Matrix4x4& asyncTransform, Layer* aLayer)
   // then applying it to container as-is will produce incorrect results. To
   // avoid this, translate the layer so that the clip rect starts at the origin,
   // apply the tree transform, and translate back.
-  if (const nsIntRect* shadowClipRect = aLayer->AsLayerComposite()->GetShadowClipRect()) {
-    if (shadowClipRect->TopLeft() != nsIntPoint()) {  // avoid a gratuitous change of basis
+  if (const Maybe<ParentLayerIntRect>& shadowClipRect = aLayer->AsLayerComposite()->GetShadowClipRect()) {
+    if (shadowClipRect->TopLeft() != ParentLayerIntPoint()) {  // avoid a gratuitous change of basis
       result.ChangeBasis(shadowClipRect->x, shadowClipRect->y, 0);
     }
   }
@@ -589,7 +587,7 @@ AsyncCompositionManager::ApplyAsyncContentTransformToTree(Layer *aLayer)
   Matrix4x4 combinedAsyncTransform;
   bool hasAsyncTransform = false;
   LayerMargin fixedLayerMargins(0, 0, 0, 0);
-  Maybe<nsIntRect> clipRect = ToMaybe(aLayer->AsLayerComposite()->GetShadowClipRect());
+  Maybe<ParentLayerIntRect> clipRect = aLayer->AsLayerComposite()->GetShadowClipRect();
 
   for (uint32_t i = 0; i < aLayer->GetFrameMetricsCount(); i++) {
     AsyncPanZoomController* controller = aLayer->GetAsyncPanZoomController(i);
@@ -639,15 +637,14 @@ AsyncCompositionManager::ApplyAsyncContentTransformToTree(Layer *aLayer)
       // bounds at that level.
       ParentLayerRect transformed = TransformTo<ParentLayerPixel>(
         (Matrix4x4(asyncTransformWithoutOverscroll) * overscrollTransform),
-        ParentLayerRect(ViewAs<ParentLayerPixel>(*clipRect)));
-      clipRect = Some(ParentLayerIntRect::ToUntyped(
-        RoundedOut(transformed.Intersect(metrics.mCompositionBounds))));
+        ParentLayerRect(*clipRect));
+      clipRect = Some(RoundedOut(transformed.Intersect(metrics.mCompositionBounds)));
     }
   }
 
   if (hasAsyncTransform) {
     if (clipRect) {
-      aLayer->AsLayerComposite()->SetShadowClipRect(clipRect.ptr());
+      aLayer->AsLayerComposite()->SetShadowClipRect(clipRect);
     }
     // Apply the APZ transform on top of GetLocalTransform() here (rather than
     // GetTransform()) in case the OMTA code in SampleAnimations already set a
diff --git a/gfx/layers/composite/LayerManagerComposite.cpp b/gfx/layers/composite/LayerManagerComposite.cpp
index 54b7c66eb1078..d634a97834f70 100644
--- a/gfx/layers/composite/LayerManagerComposite.cpp
+++ b/gfx/layers/composite/LayerManagerComposite.cpp
@@ -21,6 +21,7 @@
 #include "PaintedLayerComposite.h"      // for PaintedLayerComposite
 #include "TiledLayerBuffer.h"           // for TiledLayerComposer
 #include "Units.h"                      // for ScreenIntRect
+#include "UnitTransforms.h"             // for ViewAs
 #include "gfx2DGlue.h"                  // for ToMatrix4x4
 #include "gfxPrefs.h"                   // for gfxPrefs
 #ifdef XP_MACOSX
@@ -234,9 +235,9 @@ LayerManagerComposite::ApplyOcclusionCulling(Layer* aLayer, nsIntRegion& aOpaque
       localOpaque.Or(localOpaque, composite->GetFullyRenderedRegion());
     }
     localOpaque.MoveBy(transform2d._31, transform2d._32);
-    const nsIntRect* clip = aLayer->GetEffectiveClipRect();
+    const Maybe<ParentLayerIntRect>& clip = aLayer->GetEffectiveClipRect();
     if (clip) {
-      localOpaque.And(localOpaque, *clip);
+      localOpaque.And(localOpaque, ParentLayerIntRect::ToUntyped(*clip));
     }
     aOpaqueRegion.Or(aOpaqueRegion, localOpaque);
   }
@@ -694,7 +695,7 @@ LayerManagerComposite::Render()
     mInvalidRegion.SetEmpty();
   }
 
-  nsIntRect clipRect;
+  ParentLayerIntRect clipRect;
   Rect bounds(mRenderBounds.x, mRenderBounds.y, mRenderBounds.width, mRenderBounds.height);
   Rect actualBounds;
 
@@ -707,7 +708,7 @@ LayerManagerComposite::Render()
   } else {
     gfx::Rect rect;
     mCompositor->BeginFrame(invalid, nullptr, bounds, &rect, &actualBounds);
-    clipRect = nsIntRect(rect.x, rect.y, rect.width, rect.height);
+    clipRect = ParentLayerIntRect(rect.x, rect.y, rect.width, rect.height);
   }
 
   if (actualBounds.IsEmpty()) {
@@ -729,8 +730,8 @@ LayerManagerComposite::Render()
   }
 
   // Render our layers.
-  RootLayer()->Prepare(RenderTargetPixel::FromUntyped(clipRect));
-  RootLayer()->RenderLayer(clipRect);
+  RootLayer()->Prepare(ViewAs<RenderTargetPixel>(clipRect, PixelCastJustification::RenderTargetIsParentLayerForRoot));
+  RootLayer()->RenderLayer(ParentLayerIntRect::ToUntyped(clipRect));
 
   if (!mRegionToClear.IsEmpty()) {
     nsIntRegionRectIterator iter(mRegionToClear);
@@ -742,7 +743,7 @@ LayerManagerComposite::Render()
 
   if (mTwoPassTmpTarget) {
     MOZ_ASSERT(haveLayerEffects);
-    PopGroupForLayerEffects(previousTarget, clipRect,
+    PopGroupForLayerEffects(previousTarget, ParentLayerIntRect::ToUntyped(clipRect),
                             grayscaleVal, invertVal, contrastVal);
   }
 
@@ -1096,7 +1097,6 @@ LayerComposite::LayerComposite(LayerManagerComposite *aManager)
   : mCompositeManager(aManager)
   , mCompositor(aManager->GetCompositor())
   , mShadowOpacity(1.0)
-  , mUseShadowClipRect(false)
   , mShadowTransformSetByAnimation(false)
   , mDestroyed(false)
   , mLayerComposited(false)
diff --git a/gfx/layers/composite/LayerManagerComposite.h b/gfx/layers/composite/LayerManagerComposite.h
index 0e6552099dc21..ca5f071292640 100644
--- a/gfx/layers/composite/LayerManagerComposite.h
+++ b/gfx/layers/composite/LayerManagerComposite.h
@@ -9,6 +9,7 @@
 #include <stdint.h>                     // for int32_t, uint32_t
 #include "GLDefs.h"                     // for GLenum
 #include "Layers.h"
+#include "Units.h"                      // for ParentLayerIntRect
 #include "mozilla/Assertions.h"         // for MOZ_ASSERT, etc
 #include "mozilla/Attributes.h"         // for override
 #include "mozilla/RefPtr.h"             // for RefPtr, TemporaryRef
@@ -18,6 +19,7 @@
 #include "mozilla/gfx/Types.h"          // for SurfaceFormat
 #include "mozilla/layers/CompositorTypes.h"
 #include "mozilla/layers/LayersTypes.h"  // for LayersBackend, etc
+#include "mozilla/Maybe.h"              // for Maybe
 #include "mozilla/RefPtr.h"
 #include "mozilla/UniquePtr.h"
 #include "nsAString.h"
@@ -403,12 +405,9 @@ class LayerComposite
     mShadowOpacity = aOpacity;
   }
 
-  void SetShadowClipRect(const nsIntRect* aRect)
+  void SetShadowClipRect(const Maybe<ParentLayerIntRect>& aRect)
   {
-    mUseShadowClipRect = aRect != nullptr;
-    if (aRect) {
-      mShadowClipRect = *aRect;
-    }
+    mShadowClipRect = aRect;
   }
 
   void SetShadowTransform(const gfx::Matrix4x4& aMatrix)
@@ -432,7 +431,7 @@ class LayerComposite
 
   // These getters can be used anytime.
   float GetShadowOpacity() { return mShadowOpacity; }
-  const nsIntRect* GetShadowClipRect() { return mUseShadowClipRect ? &mShadowClipRect : nullptr; }
+  const Maybe<ParentLayerIntRect>& GetShadowClipRect() { return mShadowClipRect; }
   const nsIntRegion& GetShadowVisibleRegion() { return mShadowVisibleRegion; }
   const gfx::Matrix4x4& GetShadowTransform() { return mShadowTransform; }
   bool GetShadowTransformSetByAnimation() { return mShadowTransformSetByAnimation; }
@@ -449,11 +448,10 @@ class LayerComposite
 protected:
   gfx::Matrix4x4 mShadowTransform;
   nsIntRegion mShadowVisibleRegion;
-  nsIntRect mShadowClipRect;
+  Maybe<ParentLayerIntRect> mShadowClipRect;
   LayerManagerComposite* mCompositeManager;
   RefPtr<Compositor> mCompositor;
   float mShadowOpacity;
-  bool mUseShadowClipRect;
   bool mShadowTransformSetByAnimation;
   bool mDestroyed;
   bool mLayerComposited;
diff --git a/gfx/layers/ipc/LayerTransactionParent.cpp b/gfx/layers/ipc/LayerTransactionParent.cpp
index d8c1f9ffd987b..7d1007318cc41 100644
--- a/gfx/layers/ipc/LayerTransactionParent.cpp
+++ b/gfx/layers/ipc/LayerTransactionParent.cpp
@@ -327,7 +327,7 @@ LayerTransactionParent::RecvUpdate(InfallibleTArray<Edit>&& cset,
       layer->SetEventRegions(common.eventRegions());
       layer->SetContentFlags(common.contentFlags());
       layer->SetOpacity(common.opacity());
-      layer->SetClipRect(common.useClipRect() ? &common.clipRect() : nullptr);
+      layer->SetClipRect(common.useClipRect() ? Some(common.clipRect()) : Nothing());
       layer->SetBaseTransform(common.transform().value());
       layer->SetPostScale(common.postXScale(), common.postYScale());
       layer->SetIsFixedPosition(common.isFixedPosition());
diff --git a/gfx/layers/ipc/LayersMessages.ipdlh b/gfx/layers/ipc/LayersMessages.ipdlh
index 0176840717a38..fe5996e269361 100644
--- a/gfx/layers/ipc/LayersMessages.ipdlh
+++ b/gfx/layers/ipc/LayersMessages.ipdlh
@@ -33,6 +33,7 @@ using struct mozilla::layers::TextureInfo from "mozilla/layers/CompositorTypes.h
 using mozilla::LayerMargin from "Units.h";
 using mozilla::LayerPoint from "Units.h";
 using mozilla::LayerRect from "Units.h";
+using mozilla::ParentLayerIntRect from "Units.h";
 using mozilla::layers::ScaleMode from "mozilla/layers/LayersTypes.h";
 using mozilla::layers::EventRegions from "mozilla/layers/LayersTypes.h";
 using mozilla::layers::EventRegionsOverride from "mozilla/layers/LayersTypes.h";
@@ -204,7 +205,7 @@ struct CommonLayerAttributes {
   uint32_t contentFlags;
   float opacity;
   bool useClipRect;
-  nsIntRect clipRect;
+  ParentLayerIntRect clipRect;
   bool isFixedPosition;
   LayerPoint fixedPositionAnchor;
   LayerMargin fixedPositionMargin;
diff --git a/gfx/layers/ipc/ShadowLayers.cpp b/gfx/layers/ipc/ShadowLayers.cpp
index d9c294257c07a..6cfc9d39ca666 100644
--- a/gfx/layers/ipc/ShadowLayers.cpp
+++ b/gfx/layers/ipc/ShadowLayers.cpp
@@ -587,7 +587,7 @@ ShadowLayerForwarder::EndTransaction(InfallibleTArray<EditReply>* aReplies,
     common.opacity() = mutant->GetOpacity();
     common.useClipRect() = !!mutant->GetClipRect();
     common.clipRect() = (common.useClipRect() ?
-                         *mutant->GetClipRect() : nsIntRect());
+                         *mutant->GetClipRect() : ParentLayerIntRect());
     common.isFixedPosition() = mutant->GetIsFixedPosition();
     common.fixedPositionAnchor() = mutant->GetFixedPositionAnchor();
     common.fixedPositionMargin() = mutant->GetFixedPositionMargins();
diff --git a/gfx/tests/gtest/TestAsyncPanZoomController.cpp b/gfx/tests/gtest/TestAsyncPanZoomController.cpp
index 0496d9284c855..2f0e22b228790 100644
--- a/gfx/tests/gtest/TestAsyncPanZoomController.cpp
+++ b/gfx/tests/gtest/TestAsyncPanZoomController.cpp
@@ -19,6 +19,7 @@
 #include "base/task.h"
 #include "Layers.h"
 #include "TestLayers.h"
+#include "UnitTransforms.h"
 #include "gfxPrefs.h"
 
 using namespace mozilla;
@@ -1789,7 +1790,7 @@ class APZCTreeManagerTester : public ::testing::Test {
     metrics.SetScrollableRect(aScrollableRect);
     metrics.SetScrollOffset(CSSPoint(0, 0));
     aLayer->SetFrameMetrics(metrics);
-    aLayer->SetClipRect(&layerBound);
+    aLayer->SetClipRect(Some(ViewAs<ParentLayerPixel>(layerBound)));
     if (!aScrollableRect.IsEqualEdges(CSSRect(-1, -1, -1, -1))) {
       // The purpose of this is to roughly mimic what layout would do in the
       // case of a scrollable frame with the event regions and clip. This lets
diff --git a/layout/base/FrameLayerBuilder.cpp b/layout/base/FrameLayerBuilder.cpp
index e8dc0adf427df..c2d349a107774 100644
--- a/layout/base/FrameLayerBuilder.cpp
+++ b/layout/base/FrameLayerBuilder.cpp
@@ -7,35 +7,38 @@
 
 #include "FrameLayerBuilder.h"
 
+#include "mozilla/LookAndFeel.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/dom/ProfileTimelineMarkerBinding.h"
 #include "mozilla/gfx/Matrix.h"
-#include "nsDisplayList.h"
-#include "nsPresContext.h"
-#include "nsLayoutUtils.h"
-#include "Layers.h"
+#include "ActiveLayerTracker.h"
 #include "BasicLayers.h"
-#include "gfxUtils.h"
-#include "nsRenderingContext.h"
-#include "MaskLayerImageCache.h"
-#include "nsIScrollableFrame.h"
-#include "nsPrintfCString.h"
-#include "LayerTreeInvalidation.h"
-#include "nsSVGIntegrationUtils.h"
 #include "ImageContainer.h"
-#include "ActiveLayerTracker.h"
+#include "LayerTreeInvalidation.h"
+#include "Layers.h"
+#include "MaskLayerImageCache.h"
+#include "UnitTransforms.h"
+#include "Units.h"
 #include "gfx2DGlue.h"
-#include "mozilla/LookAndFeel.h"
+#include "gfxUtils.h"
+#include "nsDisplayList.h"
 #include "nsDocShell.h"
+#include "nsIScrollableFrame.h"
 #include "nsImageFrame.h"
-#include "mozilla/dom/ProfileTimelineMarkerBinding.h"
+#include "nsLayoutUtils.h"
+#include "nsPresContext.h"
+#include "nsPrintfCString.h"
+#include "nsRenderingContext.h"
+#include "nsSVGIntegrationUtils.h"
 
-#include "GeckoProfiler.h"
-#include "mozilla/gfx/Tools.h"
+#include "mozilla/Move.h"
+#include "mozilla/ReverseIterator.h"
 #include "mozilla/gfx/2D.h"
-#include "gfxPrefs.h"
-#include "LayersLogging.h"
+#include "mozilla/gfx/Tools.h"
 #include "mozilla/unused.h"
-#include "mozilla/ReverseIterator.h"
-#include "mozilla/Move.h"
+#include "GeckoProfiler.h"
+#include "LayersLogging.h"
+#include "gfxPrefs.h"
 
 #include <algorithm>
 
@@ -2828,11 +2831,11 @@ void ContainerState::FinishPaintedLayerData(PaintedLayerData& aData, FindOpaqueB
       imageLayer->SetPostScale(mParameters.mXScale,
                                mParameters.mYScale);
       if (data->mItemClip.HasClip()) {
-        nsIntRect clip = ScaleToNearestPixels(data->mItemClip.GetClipRect());
-        clip.MoveBy(mParameters.mOffset);
-        imageLayer->SetClipRect(&clip);
+        ParentLayerIntRect clip = ViewAs<ParentLayerPixel>(ScaleToNearestPixels(data->mItemClip.GetClipRect()));
+        clip.MoveBy(ViewAs<ParentLayerPixel>(mParameters.mOffset));
+        imageLayer->SetClipRect(Some(clip));
       } else {
-        imageLayer->SetClipRect(nullptr);
+        imageLayer->SetClipRect(Nothing());
       }
       layer = imageLayer;
       mLayerBuilder->StoreOptimizedLayerForFrame(data->mImage,
@@ -2849,7 +2852,7 @@ void ContainerState::FinishPaintedLayerData(PaintedLayerData& aData, FindOpaqueB
       nsIntRect visibleRect = data->mVisibleRegion.GetBounds();
       visibleRect.MoveBy(-GetTranslationForPaintedLayer(data->mLayer));
       colorLayer->SetBounds(visibleRect);
-      colorLayer->SetClipRect(nullptr);
+      colorLayer->SetClipRect(Nothing());
 
       layer = colorLayer;
       FLB_LOG_PAINTED_LAYER_DECISION(data, "  Selected color layer=%p\n", layer.get());
@@ -2868,15 +2871,15 @@ void ContainerState::FinishPaintedLayerData(PaintedLayerData& aData, FindOpaqueB
 
     // Hide the PaintedLayer. We leave it in the layer tree so that we
     // can find and recycle it later.
-    nsIntRect emptyRect;
-    data->mLayer->SetClipRect(&emptyRect);
+    ParentLayerIntRect emptyRect;
+    data->mLayer->SetClipRect(Some(emptyRect));
     data->mLayer->SetVisibleRegion(nsIntRegion());
     data->mLayer->InvalidateRegion(data->mLayer->GetValidRegion().GetBounds());
     data->mLayer->SetEventRegions(EventRegions());
   } else {
     layer = data->mLayer;
     imageContainer = nullptr;
-    layer->SetClipRect(nullptr);
+    layer->SetClipRect(Nothing());
     FLB_LOG_PAINTED_LAYER_DECISION(data, "  Selected painted layer=%p\n", layer.get());
   }
 
@@ -3508,15 +3511,15 @@ ContainerState::ProcessDisplayItems(nsDisplayList* aList)
     nsIntRect itemDrawRect = ScaleToOutsidePixels(itemContent, snap);
     bool prerenderedTransform = itemType == nsDisplayItem::TYPE_TRANSFORM &&
         static_cast<nsDisplayTransform*>(item)->ShouldPrerender(mBuilder);
-    nsIntRect clipRect;
+    ParentLayerIntRect clipRect;
     const DisplayItemClip& itemClip = item->GetClip();
     if (itemClip.HasClip()) {
       itemContent.IntersectRect(itemContent, itemClip.GetClipRect());
-      clipRect = ScaleToNearestPixels(itemClip.GetClipRect());
+      clipRect = ViewAs<ParentLayerPixel>(ScaleToNearestPixels(itemClip.GetClipRect()));
       if (!prerenderedTransform) {
-        itemDrawRect.IntersectRect(itemDrawRect, clipRect);
+        itemDrawRect.IntersectRect(itemDrawRect, ParentLayerIntRect::ToUntyped(clipRect));
       }
-      clipRect.MoveBy(mParameters.mOffset);
+      clipRect.MoveBy(ViewAs<ParentLayerPixel>(mParameters.mOffset));
     }
 #ifdef DEBUG
     nsRect bounds = itemContent;
@@ -3614,7 +3617,11 @@ ContainerState::ProcessDisplayItems(nsDisplayList* aList)
       // visible rect for the two important cases.
       nscolor uniformColor = NS_RGBA(0,0,0,0);
       nscolor* uniformColorPtr = !mayDrawOutOfOrder ? &uniformColor : nullptr;
-      nsIntRect* clipPtr = itemClip.HasClip() ? &clipRect : nullptr;
+      nsIntRect clipRectUntyped;
+      nsIntRect* clipPtr = itemClip.HasClip() ? &clipRectUntyped : nullptr;
+      if (clipPtr) {
+	      clipRectUntyped = ParentLayerIntRect::ToUntyped(clipRect);
+      }
       if (animatedGeometryRoot == item->Frame() &&
           animatedGeometryRoot != mBuilder->RootReferenceFrame()) {
         // This is the case for scrollbar thumbs, for example. In that case the
@@ -3622,10 +3629,12 @@ ContainerState::ProcessDisplayItems(nsDisplayList* aList)
         const nsIFrame* clipAnimatedGeometryRoot =
           mPaintedLayerDataTree.GetParentAnimatedGeometryRoot(animatedGeometryRoot);
         mPaintedLayerDataTree.AddingOwnLayer(clipAnimatedGeometryRoot,
-                                             clipPtr, uniformColorPtr);
+					     clipPtr,
+					     uniformColorPtr);
       } else if (prerenderedTransform) {
         mPaintedLayerDataTree.AddingOwnLayer(animatedGeometryRoot,
-                                             clipPtr, uniformColorPtr);
+					     clipPtr,
+					     uniformColorPtr);
       } else {
         // Using itemVisibleRect here isn't perfect. itemVisibleRect can be
         // larger or smaller than the potential bounds of item's contents in
@@ -3680,9 +3689,9 @@ ContainerState::ProcessDisplayItems(nsDisplayList* aList)
                    "If we have rounded rects, we must have a clip rect");
       // It has its own layer. Update that layer's clip and visible rects.
       if (itemClip.HasClip()) {
-        ownLayer->SetClipRect(&clipRect);
+        ownLayer->SetClipRect(Some(clipRect));
       } else {
-        ownLayer->SetClipRect(nullptr);
+        ownLayer->SetClipRect(Nothing());
       }
 
       // rounded rectangle clipping using mask layers
@@ -4225,8 +4234,8 @@ ContainerState::SetupScrollingMetadata(NewLayerEntry* aEntry)
   }
   uint32_t baseLength = metricsArray.Length();
 
-  nsIntRect tmpClipRect;
-  const nsIntRect* layerClip = aEntry->mLayer->GetClipRect();
+  ParentLayerIntRect tmpClipRect;
+  const ParentLayerIntRect* layerClip = aEntry->mLayer->GetClipRect().ptrOr(nullptr);
   nsIFrame* fParent;
   for (const nsIFrame* f = aEntry->mAnimatedGeometryRoot;
        f != mContainerAnimatedGeometryRoot;
@@ -4255,7 +4264,7 @@ ContainerState::SetupScrollingMetadata(NewLayerEntry* aEntry)
     scrollFrame->ComputeFrameMetrics(aEntry->mLayer, mContainerReferenceFrame,
                                      mParameters, &clipRect, &metricsArray);
     if (clipRect.width >= 0) {
-      nsIntRect pixClip = ScaleToNearestPixels(clipRect);
+      ParentLayerIntRect pixClip = ViewAs<ParentLayerPixel>(ScaleToNearestPixels(clipRect));
       if (layerClip) {
         tmpClipRect.IntersectRect(pixClip, *layerClip);
       } else {
@@ -4267,7 +4276,7 @@ ContainerState::SetupScrollingMetadata(NewLayerEntry* aEntry)
       // both CSS and scroll clipping.
     }
   }
-  aEntry->mLayer->SetClipRect(layerClip);
+  aEntry->mLayer->SetClipRect(ToMaybe(layerClip));
   // Watch out for FrameMetrics copies in profiles
   aEntry->mLayer->SetFrameMetrics(metricsArray);
 }
@@ -4298,9 +4307,9 @@ ContainerState::PostprocessRetainedLayers(nsIntRegion* aOpaqueRegionForContainer
     if (hideAll) {
       e->mVisibleRegion.SetEmpty();
     } else if (!e->mLayer->IsScrollbarContainer()) {
-      const nsIntRect* clipRect = e->mLayer->GetClipRect();
+      const Maybe<ParentLayerIntRect>& clipRect = e->mLayer->GetClipRect();
       if (clipRect && opaqueRegionForContainer >= 0 &&
-          opaqueRegions[opaqueRegionForContainer].mOpaqueRegion.Contains(*clipRect)) {
+          opaqueRegions[opaqueRegionForContainer].mOpaqueRegion.Contains(ParentLayerIntRect::ToUntyped(*clipRect))) {
         e->mVisibleRegion.SetEmpty();
       } else if (data) {
         e->mVisibleRegion.Sub(e->mVisibleRegion, data->mOpaqueRegion);
@@ -4333,9 +4342,9 @@ ContainerState::PostprocessRetainedLayers(nsIntRegion* aOpaqueRegionForContainer
       }
 
       nsIntRegion clippedOpaque = e->mOpaqueRegion;
-      const nsIntRect* clipRect = e->mLayer->GetClipRect();
+      const Maybe<ParentLayerIntRect>& clipRect = e->mLayer->GetClipRect();
       if (clipRect) {
-        clippedOpaque.AndWith(*clipRect);
+        clippedOpaque.AndWith(ParentLayerIntRect::ToUntyped(*clipRect));
       }
       data->mOpaqueRegion.Or(data->mOpaqueRegion, clippedOpaque);
       if (e->mHideAllLayersBelow) {
diff --git a/layout/base/UnitTransforms.h b/layout/base/UnitTransforms.h
index 0b9dfc442dc38..37485510530f6 100644
--- a/layout/base/UnitTransforms.h
+++ b/layout/base/UnitTransforms.h
@@ -22,6 +22,8 @@ namespace mozilla {
 enum class PixelCastJustification : uint8_t {
   // For the root layer, Screen Pixel = Parent Layer Pixel.
   ScreenIsParentLayerForRoot,
+  // For the root layer, Render Target Pixel = Parent Layer Pixel.
+  RenderTargetIsParentLayerForRoot,
   // For the root composition size we want to view it as layer pixels in any layer
   ParentLayerToLayerForRootComposition,
   // The Layer coordinate space for one layer is the ParentLayer coordinate
@@ -54,6 +56,14 @@ template <class TargetUnits, class SourceUnits>
 gfx::IntPointTyped<TargetUnits> ViewAs(const gfx::IntPointTyped<SourceUnits>& aPoint, PixelCastJustification) {
   return gfx::IntPointTyped<TargetUnits>(aPoint.x, aPoint.y);
 }
+template <class TargetUnits, class SourceUnits>
+gfx::RectTyped<TargetUnits> ViewAs(const gfx::RectTyped<SourceUnits>& aRect, PixelCastJustification) {
+  return gfx::RectTyped<TargetUnits>(aRect.x, aRect.y, aRect.width, aRect.height);
+}
+template <class TargetUnits, class SourceUnits>
+gfx::IntRectTyped<TargetUnits> ViewAs(const gfx::IntRectTyped<SourceUnits>& aRect, PixelCastJustification) {
+  return gfx::IntRectTyped<TargetUnits>(aRect.x, aRect.y, aRect.width, aRect.height);
+}
 template <class NewTargetUnits, class OldTargetUnits, class SourceUnits>
 gfx::ScaleFactor<SourceUnits, NewTargetUnits> ViewTargetAs(
     const gfx::ScaleFactor<SourceUnits, OldTargetUnits>& aScaleFactor,