Bug 1622395 - Use AutoApplyAsyncTestAttributes instead of manually doing a half-job. r=botond

The code in GetVisibleRect() uses the test scroll offset, but not the test zoom.
Using AutoApplyAsyncTestAttributes automatically uses both.

Differential Revision: https://phabricator.services.mozilla.com/D66956

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

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -4319,9 +4319,9 @@ Matrix4x4 AsyncPanZoomController::GetTransformToLastDispatchedPaint() const {
 
 CSSRect AsyncPanZoomController::GetVisibleRect(
     const RecursiveMutexAutoLock& aProofOfLock) const {
+  AutoApplyAsyncTestAttributes testAttributeApplier(this, aProofOfLock);
   CSSPoint currentScrollOffset =
-      GetEffectiveScrollOffset(AsyncPanZoomController::eForCompositing) +
-      mTestAsyncScrollOffset;
+      GetEffectiveScrollOffset(AsyncPanZoomController::eForCompositing);
   CSSRect visible = CSSRect(currentScrollOffset,
                             Metrics().CalculateCompositedSizeInCssPixels());
   return visible;