Implement CSSOM Smooth Scroll API

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 0bd1c8d990a0c3f36aa18c470d29a5291f5642d0..9f0a8c0b50fdb559092fdf9cb8a6329f226b59bf 100644
--- a/Source/platform/graphics/GraphicsLayer.cpp
+++ b/Source/platform/graphics/GraphicsLayer.cpp
@@ -1105,15 +1105,22 @@ void GraphicsLayer::paint(GraphicsContext& context, const IntRect& clip)
 }
 
 
-void GraphicsLayer::notifyAnimationStarted(double monotonicTime, WebAnimation::TargetProperty)
+void GraphicsLayer::notifyAnimationStarted(double monotonicTime, WebAnimation::TargetProperty targetProperty)
 {
+    if (targetProperty == WebAnimation::TargetPropertyScrollOffset) {
+        if (m_scrollableArea)
+            m_scrollableArea->notifyAnimationStarted(monotonicTime);
+        return;
+    }
     if (m_client)
         m_client->notifyAnimationStarted(this, monotonicTime);
 }
 
-void GraphicsLayer::notifyAnimationFinished(double, WebAnimation::TargetProperty)
+void GraphicsLayer::notifyAnimationFinished(double monotonicTime, WebAnimation::TargetProperty targetProperty)
 {
-    // Do nothing.
+    if (targetProperty == WebAnimation::TargetPropertyScrollOffset && m_scrollableArea) {
+        m_scrollableArea->notifyAnimationFinished(monotonicTime);
+    }
 }
 
 void GraphicsLayer::didScroll()