Add WebView API for smoothScroll

public/web/WebView.h

 /*
  * Copyright (C) 2009, 2010, 2011, 2012 Google 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 158 matching lines @@
 
     // Clears the focused element (and selection if a text field is focused)
     // to ensure that a text field on the page is not eating keystrokes we
     // send it.
     virtual void clearFocusedElement() = 0;
 
     // Scrolls the node currently in focus into |rect|, where |rect| is in
     // viewport space. Returns true if an animation was started.
     virtual bool scrollFocusedNodeIntoRect(const WebRect&) { return false; }
 
+    // Smooth scroll the root layer to |targetX|, |targetY| in |durationMs|.
+    virtual void smoothScroll(int targetX, int targetY, long durationMs) { }
+
     // Advance the focus of the WebView forward to the next element or to the
     // previous element in the tab sequence (if reverse is true).
     virtual void advanceFocus(bool reverse) { }
 
     // Animate a scale into the specified rect where multiple targets were
     // found from previous tap gesture.
     // Returns false if it doesn't do any zooming.
     virtual bool zoomToMultipleTargetsRect(const WebRect&) = 0;
 
 
@@ skipping 280 matching lines @@
     // context's ability to deal with that failure gracefully can be tested.
     virtual void forceNextDrawingBufferCreationToFail() = 0;
 
 protected:
     ~WebView() {}
 };
 
 } // namespace blink
 
 #endif