Bug 1636273. Fix calculation of scroll position in AsyncPanZoomContro…

…ller::HandleDragEvent. r=kats,botond

The scroll position and scrollable rect are inside the zoom boundary so we need to use the composisted size inside the zoom boundary as well.

Differential Revision: https://phabricator.services.mozilla.com/D76089

gfx/2d/BaseSize.h

@@ -42,6 +42,9 @@ struct BaseSize {
 
   bool IsSquare() const { return width == height; }
 
+  MOZ_ALWAYS_INLINE T Width() const { return width; }
+  MOZ_ALWAYS_INLINE T Height() const { return height; }
+
   // Note that '=' isn't defined so we'll get the
   // compiler generated default assignment operator
 

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1088,10 +1088,8 @@ nsEventStatus AsyncPanZoomController::HandleDragEvent(
       GetAxisStart(direction, Metrics().GetScrollableRect().TopLeft());
   CSSCoord maxScrollPosition =
       GetAxisStart(direction, Metrics().GetScrollableRect().BottomRight()) -
-      GetAxisLength(
-          direction,
-          Metrics()
-              .CalculateCompositionBoundsInCssPixelsOfSurroundingContent());
+      GetAxisLength(direction,
+                    Metrics().CalculateCompositedSizeInCssPixels());
   CSSCoord scrollPosition =
       minScrollPosition +
       (scrollPercent * (maxScrollPosition - minScrollPosition));

layout/base/Units.h

@@ -828,6 +828,11 @@ struct CoordOfImpl<gfx::IntRectTyped<Units>> {
   typedef gfx::IntCoordTyped<Units> Type;
 };
 
+template <typename Units>
+struct CoordOfImpl<gfx::SizeTyped<Units>> {
+  typedef gfx::CoordTyped<Units> Type;
+};
+
 template <typename T>
 using CoordOf = typename CoordOfImpl<T>::Type;