Support buttons attribute for drag event (blink side).

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 325 matching lines @@
 
     // Notfies the WebView that the system drag and drop operation has ended.
     virtual void dragSourceSystemDragEnded() = 0;
 
     // Callback methods when a drag-and-drop operation is trying to drop
     // something on the WebView.
     virtual WebDragOperation dragTargetDragEnter(
         const WebDragData&,
         const WebPoint& clientPoint, const WebPoint& screenPoint,
         WebDragOperationsMask operationsAllowed,
-        int keyModifiers) = 0;
+        int modifiers) = 0;
     virtual WebDragOperation dragTargetDragOver(
         const WebPoint& clientPoint, const WebPoint& screenPoint,
         WebDragOperationsMask operationsAllowed,
-        int keyModifiers) = 0;
+        int modifiers) = 0;
     virtual void dragTargetDragLeave() = 0;
     virtual void dragTargetDrop(
         const WebPoint& clientPoint, const WebPoint& screenPoint,
-        int keyModifiers) = 0;
+        int modifiers) = 0;
 
     // Retrieves a list of spelling markers.
     virtual void spellingMarkers(WebVector<uint32_t>* markers) = 0;
     virtual void removeSpellingMarkersUnderWords(const WebVector<WebString>& words) = 0;
 
     // Support for resource loading initiated by plugins -------------------
 
     // Returns next unused request identifier which is unique within the
     // parent Page.
     virtual unsigned long createUniqueIdentifierForRequest() = 0;
@@ skipping 124 matching lines @@
     // event gets generated/tested.
     virtual void forceNextWebGLContextCreationToFail() = 0;
 
 protected:
     ~WebView() {}
 };
 
 } // namespace blink
 
 #endif