Remove ScrollableArea::notifyScrollPositionChanged and cleanup scroll animators.

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 0123bd8b8a801a95db60609bec8c4ec2381e584a..bacad1536d9b729b5fa76adf64b15642aaf3a415 100644
--- a/Source/platform/scroll/ScrollableArea.h
+++ b/Source/platform/scroll/ScrollableArea.h
@@ -89,10 +89,6 @@ public:
     // cenetered in the second rect, which is given relative to the area's origin.
     void scrollIntoRect(const LayoutRect& rectInContent, const FloatRect& targetRectInFrame);
 
-    // 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 DoublePoint&);
-
     static bool scrollBehaviorFromString(const String&, ScrollBehavior&);
 
     virtual ScrollResult handleWheel(const PlatformWheelEvent&);
@@ -272,6 +268,7 @@ public:
 
     void layerForScrollingDidChange();
 
+    void cancelScrollAnimation();
     void cancelProgrammaticScrollAnimation();
 
     virtual ~ScrollableArea();
@@ -306,13 +303,12 @@ protected:
     void setScrollOrigin(const IntPoint&);
     void resetScrollOriginChanged() { m_scrollOriginChanged = false; }
 
-private:
-    void scrollPositionChanged(const DoublePoint&, ScrollType);
-
-    // NOTE: Only called from the ScrollAnimator.
+    // Needed to let the animators call scrollPositionChanged.
     friend class ScrollAnimator;
-    void setScrollOffsetFromAnimation(const DoublePoint&, ScrollType);
+    friend class ProgrammaticScrollAnimator;
+    void scrollPositionChanged(const DoublePoint&, ScrollType);
 
+private:
     void programmaticScrollHelper(const DoublePoint&, ScrollBehavior);
     void userScrollHelper(const DoublePoint&, ScrollBehavior);