Bug 1573343 - Reset the transform in a better place. r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D41672

--HG--
extra : moz-landing-system : lando

gfx/layers/basic/BasicCompositor.cpp

@@ -1033,6 +1033,9 @@ void BasicCompositor::EndFrame() {
   // Pop aInvalidregion
   mRenderTarget->mDrawTarget->PopClip();
 
+  // Reset the translation that was applied in BeginFrame.
+  mRenderTarget->mDrawTarget->SetTransform(gfx::Matrix());
+
   TryToEndRemoteDrawing();
 
   // If we are no longer recording a profile, we can drop the render target if

widget/CompositorWidget.cpp

@@ -39,7 +39,6 @@ already_AddRefed<gfx::DrawTarget> CompositorWidget::GetBackBufferDrawTarget(
       mLastBackBuffer->GetFormat() == format &&
       mLastBackBuffer->GetSize() == clientSize) {
     target = mLastBackBuffer;
-    target->SetTransform(gfx::Matrix());
     if (!aClearRect.IsEmpty()) {
       gfx::IntRect clearRect =
           aClearRect.ToUnknownRect() - aRect.ToUnknownRect().TopLeft();