Simplify platform_canvas.h by recognizing that PlatformCanvas does not actually extend

ppapi/proxy/ppb_image_data_proxy.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_PPB_IMAGE_DATA_PROXY_H_
 #define PPAPI_PPB_IMAGE_DATA_PROXY_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/shared_memory.h"
 #include "build/build_config.h"
@@ skipping 39 matching lines @@
 
   // Resource overrides.
   virtual ppapi::thunk::PPB_ImageData_API* AsPPB_ImageData_API() OVERRIDE;
   virtual void LastPluginRefWasDeleted() OVERRIDE;
 
   // PPB_ImageData API.
   virtual PP_Bool Describe(PP_ImageDataDesc* desc) OVERRIDE;
   virtual void* Map() OVERRIDE;
   virtual void Unmap() OVERRIDE;
   virtual int32_t GetSharedMemory(int* handle, uint32_t* byte_count) OVERRIDE;
-  virtual skia::PlatformCanvas* GetPlatformCanvas() OVERRIDE;
+  virtual SkCanvas* GetPlatformCanvas() OVERRIDE;
   virtual SkCanvas* GetCanvas() OVERRIDE;
 
   const PP_ImageDataDesc& desc() const { return desc_; }
 
   void set_used_in_replace_contents() { used_in_replace_contents_ = true; }
 
   // Prepares this image data to be recycled to the plugin. The contents will be
   // cleared if zero_contents is set.
   void RecycleToPlugin(bool zero_contents);
 
 #if !defined(OS_NACL)
   static ImageHandle NullHandle();
   static ImageHandle HandleFromInt(int32_t i);
 #endif
 
  private:
   PP_ImageDataDesc desc_;
 
 #if defined(OS_NACL)
   base::SharedMemory shm_;
   uint32 size_;
   int map_count_;
 #else
   scoped_ptr<TransportDIB> transport_dib_;
 
   // Null when the image isn't mapped.
-  scoped_ptr<skia::PlatformCanvas> mapped_canvas_;
+  scoped_ptr<SkCanvas> mapped_canvas_;
 #endif
 
   // Set to true when this ImageData has been used in a call to
   // Graphics2D.ReplaceContents. This is used to signal that it can be cached.
   bool used_in_replace_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageData);
 };
 
 class PPB_ImageData_Proxy : public InterfaceProxy {
@@ skipping 31 matching lines @@
   // Host->Plugin message handlers.
   void OnPluginMsgNotifyUnusedImageData(const HostResource& old_image_data);
 
   DISALLOW_COPY_AND_ASSIGN(PPB_ImageData_Proxy);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PPB_IMAGE_DATA_PROXY_H_