Implement HiDPI support in Pepper dev interface

ppapi/cpp/graphics_2d.h

 // Copyright (c) 2012 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_GRAPHICS_2D_H_
 #define PPAPI_CPP_GRAPHICS_2D_H_
 
 #include "ppapi/c/pp_stdint.h"
 #include "ppapi/cpp/resource.h"
 #include "ppapi/cpp/size.h"
@@ skipping 242 matching lines @@
   /// not issued its callback yet.  In the failure case, nothing will be
   /// updated and no callback will be scheduled.
 
   // TODO(darin): We should ensure that the completion callback always runs, so
   // that it is easier for consumers to manage memory referenced by a callback.
 
   // TODO(): Add back in the synchronous mode description once we have support
   // for it.
   int32_t Flush(const CompletionCallback& cc);
 
- private:
+ protected:
   Size size_;
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_GRAPHICS_2D_H_