Add a callback from Blink to Chromium for when page scale changes

public/web/WebViewClient.h

 /*
  * Copyright (C) 2009 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 231 matching lines @@
     // Zoom ----------------------------------------------------------------
 
     // Informs the browser that the zoom levels for this frame have changed from
     // the default values.
     virtual void zoomLimitsChanged(double minimumLevel, double maximumLevel) { }
 
     // Informs the browser that the zoom level has changed as a result of an
     // action that wasn't initiated by the client.
     virtual void zoomLevelChanged() { }
 
+    // Informs the browser that the page scale has changed.
+    virtual void pageScaleFactorChanged() { }
 
     // Navigator Content Utils  --------------------------------------------
 
     // Registers a new URL handler for the given protocol.
     virtual void registerProtocolHandler(const WebString& scheme,
         const WebURL& url,
         const WebString& title) { }
 
     // Unregisters a given URL handler for the given protocol.
     virtual void unregisterProtocolHandler(const WebString& scheme, const WebURL& url) { }
@@ skipping 33 matching lines @@
     // Informs the browser that the draggable regions have been updated.
     virtual void draggableRegionsChanged() { }
 
 protected:
     ~WebViewClient() { }
 };
 
 } // namespace blink
 
 #endif