Clarify/fix fullscreen semantics, and add GetScreenSize

ppapi/cpp/dev/fullscreen_dev.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_CPP_DEV_FULLSCREEN_DEV_H_
 #define PPAPI_CPP_DEV_FULLSCREEN_DEV_H_
 
-#include <string>
-
-#include "ppapi/c/dev/ppb_fullscreen_dev.h"
-
 namespace pp {
 
 class Instance;
+class Size;
 
 class Fullscreen_Dev {
  public:
   Fullscreen_Dev(Instance* instance);
   virtual ~Fullscreen_Dev();
 
   // PPB_Fullscreen_Dev methods.
   bool IsFullscreen();
   bool SetFullscreen(bool fullscreen);
+  bool GetScreenSize(Size* size);
 
  private:
-  Instance* associated_instance_;
+  Instance* instance_;
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_FULLSCREEN_DEV_H_