Implement CSSOM smooth scroll for Elements

Source/platform/scroll/ScrollableArea.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 412 matching lines @@
 {
     if (HostWindow* window = hostWindow()) {
         window->scheduleAnimation();
         return true;
     }
     return false;
 }
 
 void ScrollableArea::serviceScrollAnimations(double monotonicTime)
 {
-    if (ScrollAnimator* scrollAnimator = existingScrollAnimator())
+    bool hasRunningAnimation = false;
+    if (ScrollAnimator* scrollAnimator = existingScrollAnimator()) {
         scrollAnimator->serviceScrollAnimations();
-    if (ProgrammaticScrollAnimator* programmaticScrollAnimator = existingProgrammaticScrollAnimator())
+        if (scrollAnimator->hasRunningAnimation())
+            hasRunningAnimation = true;
+    }
+    if (ProgrammaticScrollAnimator* programmaticScrollAnimator = existingProgrammaticScrollAnimator()) {
         programmaticScrollAnimator->tickAnimation(monotonicTime);
+        if (programmaticScrollAnimator->hasRunningAnimation())
+            hasRunningAnimation = true;
+    }
+    if (!hasRunningAnimation)
+        deregisterForAnimation();
 }
 
 void ScrollableArea::cancelProgrammaticScrollAnimation()
 {
     if (ProgrammaticScrollAnimator* programmaticScrollAnimator = existingProgrammaticScrollAnimator())
         programmaticScrollAnimator->cancelAnimation();
 }
 
 IntRect ScrollableArea::visibleContentRect(IncludeScrollbarsInRect scrollbarInclusion) const
 {
@@ skipping 36 matching lines @@
 {
     return scrollSize(orientation);
 }
 
 float ScrollableArea::pixelStep(ScrollbarOrientation) const
 {
     return 1;
 }
 
 } // namespace blink