Add enterFullscreen/exitFullscreen to WebFrameClient.

public/web/WebFrameClient.h

 /*
  * Copyright (C) 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 574 matching lines @@
     // Returns an identifier of the service worker controlling the document
     // associated with the WebDataSource.
     virtual int64_t serviceWorkerID(WebDataSource&) { return -1; }
 
 
     // Speech --------------------------------------------------------------
 
     // Access the embedder API for speech recognition services.
     virtual WebSpeechRecognizer* speechRecognizer() { return 0; }
 
+
+    // Fullscreen ----------------------------------------------------------
+
+    // Called to enter/exit fullscreen mode. If enterFullScreen returns true,
+    // then WebWidget::{will,Did}EnterFullScreen should bound resizing the
+    // WebWidget into fullscreen mode. Similarly, when exitFullScreen is
+    // called, WebWidget::{will,Did}ExitFullScreen should bound resizing the
+    // WebWidget out of fullscreen mode.
+    virtual bool enterFullscreen() { return false; }
+    virtual bool exitFullscreen() { return false; }
+
 protected:
     virtual ~WebFrameClient() { }
 };
 
 } // namespace blink
 
 #endif