Run smooth scroll animations on the compositor when possible

third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp

Index: third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp b/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
index f4a0af17641114168a3acfc23552c684be800f1c..695718ddd33e28c9bddcf78fb6e97fb984b9d00d 100644
--- a/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
@@ -65,6 +65,12 @@ void ProgrammaticScrollAnimator::animateToOffset(FloatPoint offset)
     m_runState = RunState::WaitingToSendToCompositor;
 }
 
+void ProgrammaticScrollAnimator::cancelAnimation()
+{
+    ASSERT(m_runState != RunState::RunningOnCompositorButNeedsUpdate);
+    ScrollAnimatorCompositorCoordinator::cancelAnimation();
+}
+
 void ProgrammaticScrollAnimator::tickAnimation(double monotonicTime)
 {
     if (m_runState != RunState::RunningOnMainThread)
@@ -155,6 +161,7 @@ void ProgrammaticScrollAnimator::layerForCompositedScrollingDidChange(WebComposi
 
 void ProgrammaticScrollAnimator::notifyCompositorAnimationFinished(int groupId)
 {
+    ASSERT(m_runState != RunState::RunningOnCompositorButNeedsUpdate);
     ScrollAnimatorCompositorCoordinator::compositorAnimationFinished(groupId);
 }