Adds a gfx_export.h to ui/gfx and converts all code in ui/gfx to

ui/gfx/image/image_png_rep.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 UI_GFX_IMAGE_IMAGE_PNG_REP_H_
 #define UI_GFX_IMAGE_IMAGE_PNG_REP_H_
 
 #include "base/memory/ref_counted_memory.h"
 #include "ui/base/layout.h"
-#include "ui/base/ui_export.h"
+#include "ui/gfx/gfx_export.h"
 
 namespace gfx {
 class Size;
 
 // An ImagePNGRep represents a bitmap's png encoded data and the scale factor it
 // was intended for.
 struct UI_EXPORT ImagePNGRep {
   ImagePNGRep();
   ImagePNGRep(const scoped_refptr<base::RefCountedMemory>& data,
               ui::ScaleFactor data_scale_factor);
   ~ImagePNGRep();
 
   // Width and height of the image, in pixels.
   // If the image is invalid, returns gfx::Size(0, 0).
   // Warning: This operation processes the entire image stream, so its result
   // should be cached if it is needed multiple times.
   gfx::Size Size() const;
 
   scoped_refptr<base::RefCountedMemory> raw_data;
   ui::ScaleFactor scale_factor;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_IMAGE_IMAGE_PNG_REP_H_