Run CSSOM smooth scroll animations on the compositor when possible

Source/platform/graphics/GraphicsLayer.cpp

Index: Source/platform/graphics/GraphicsLayer.cpp
diff --git a/Source/platform/graphics/GraphicsLayer.cpp b/Source/platform/graphics/GraphicsLayer.cpp
index 8ded5786aeb13716b7758912872265f5c089c28f..92fb981e15aaff4962f619e654a319342dc30e26 100644
--- a/Source/platform/graphics/GraphicsLayer.cpp
+++ b/Source/platform/graphics/GraphicsLayer.cpp
@@ -1085,16 +1085,19 @@ void GraphicsLayer::notifyAnimationStarted(double monotonicTime, int group)
         m_client->notifyAnimationStarted(this, monotonicTime, group);
 }
 
-void GraphicsLayer::notifyAnimationFinished(double, int)
+void GraphicsLayer::notifyAnimationFinished(double, int group)
 {
+    if (m_scrollableArea)
+        m_scrollableArea->notifyCompositorAnimationFinished(group);
 }
 
 void GraphicsLayer::didScroll()
 {
     if (m_scrollableArea) {
         DoublePoint newPosition = m_scrollableArea->minimumScrollPosition() + toDoubleSize(m_layer->layer()->scrollPositionDouble());
+        bool cancelProgrammaticAnimations = false;
         // FIXME: Remove the toFloatPoint(). crbug.com/414283.
-        m_scrollableArea->scrollToOffsetWithoutAnimation(toFloatPoint(newPosition));
+        m_scrollableArea->scrollToOffsetWithoutAnimation(toFloatPoint(newPosition), cancelProgrammaticAnimations);
     }
 }