Implement CSSOM Smooth Scroll API

Source/platform/scroll/ScrollableArea.h

Index: Source/platform/scroll/ScrollableArea.h
diff --git a/Source/platform/scroll/ScrollableArea.h b/Source/platform/scroll/ScrollableArea.h
index 15b27b7cc4fd541aac0935766f7f9d4bf5c1dff8..d3b774d60409276b6053eba7d9c104e2b92c6b45 100644
--- a/Source/platform/scroll/ScrollableArea.h
+++ b/Source/platform/scroll/ScrollableArea.h
@@ -39,6 +39,7 @@ class GraphicsContext;
 class GraphicsLayer;
 class PlatformGestureEvent;
 class PlatformWheelEvent;
+class ProgrammaticScrollAnimator;
 class ScrollAnimator;
 
 enum ScrollBehavior {
@@ -63,6 +64,8 @@ public:
     void scrollToOffsetWithoutAnimation(const FloatPoint&);
     void scrollToOffsetWithoutAnimation(ScrollbarOrientation, float offset);
 
+    void programmaticallyScrollSmoothlyToOffset(const FloatPoint&);
+
     // Should be called when the scroll position changes externally, for example if the scroll layer position
     // is updated on the scrolling thread and we need to notify the main thread.
     void notifyScrollPositionChanged(const IntPoint&);
@@ -111,6 +114,12 @@ public:
     // This getter will return null if the ScrollAnimator hasn't been created yet.
     ScrollAnimator* existingScrollAnimator() const { return m_scrollAnimator.get(); }
 
+    ProgrammaticScrollAnimator* programmaticScrollAnimator() const;
+    ProgrammaticScrollAnimator* existingProgrammaticScrollAnimator() const
+    {
+        return m_programmaticScrollAnimator.get();
+    }
+
     const IntPoint& scrollOrigin() const { return m_scrollOrigin; }
     bool scrollOriginChanged() const { return m_scrollOriginChanged; }
 
@@ -178,8 +187,10 @@ public:
 
     // Let subclasses provide a way of asking for and servicing scroll
     // animations.
+    virtual void registerForAnimation() { }
+    virtual void deregisterForAnimation() { }
     virtual bool scheduleAnimation() { return false; }
-    void serviceScrollAnimations();
+    virtual void serviceScrollAnimations(double monotonicTime);
 
     virtual bool usesCompositedScrolling() const { return false; }
 
@@ -189,6 +200,14 @@ public:
     virtual bool userInputScrollable(ScrollbarOrientation) const = 0;
     virtual bool shouldPlaceVerticalScrollbarOnLeft() const = 0;
 
+    // Notifications for compositor-driven animations.
+    void notifyAnimationStarted(double monotonicTime);
+    void notifyAnimationFinished(double monotonicTime);
+
+    void layerForScrollingDidChange();
+    void requiresMainThreadScrollingDidChange();
+    bool canUseCompositedScrollAnimations() const;
+
     // Convenience functions
     int scrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? scrollPosition().x() : scrollPosition().y(); }
     int minimumScrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? minimumScrollPosition().x() : minimumScrollPosition().y(); }
@@ -224,6 +243,8 @@ public:
     bool hasLayerForVerticalScrollbar() const;
     bool hasLayerForScrollCorner() const;
 
+    void cancelProgrammaticScrollAnimation();
+
 protected:
     ScrollableArea();
     virtual ~ScrollableArea();
@@ -258,6 +279,7 @@ private:
     virtual float pixelStep(ScrollbarOrientation) const;
 
     mutable OwnPtr<ScrollAnimator> m_scrollAnimator;
+    mutable OwnPtr<ProgrammaticScrollAnimator> m_programmaticScrollAnimator;
     unsigned m_constrainsScrollingToContentEdge : 1;
 
     unsigned m_inLiveResize : 1;