Refactor gpu::Buffer to allow different types of backing

ppapi/proxy/ppapi_command_buffer_proxy.cc

 // 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.
 
 #include "ppapi/proxy/ppapi_command_buffer_proxy.h"
 
 #include "ppapi/proxy/ppapi_messages.h"
 #include "ppapi/proxy/proxy_channel.h"
 #include "ppapi/shared_impl/api_id.h"
 #include "ppapi/shared_impl/host_resource.h"
@@ skipping 118 matching lines @@
   scoped_ptr<base::SharedMemory> shared_memory(
       new base::SharedMemory(handle.shmem(), false));
 
   // Map the shared memory on demand.
   if (!shared_memory->memory()) {
     if (!shared_memory->Map(handle.size())) {
       return NULL;
     }
   }
 
-  scoped_refptr<gpu::Buffer> buffer =
-      new gpu::Buffer(shared_memory.Pass(), handle.size());
-  return buffer;
+  return gpu::MakeBufferFromSharedMemory(shared_memory.Pass(), handle.size());
 }
 
 void PpapiCommandBufferProxy::DestroyTransferBuffer(int32 id) {
   if (last_state_.error != gpu::error::kNoError)
     return;
 
   Send(new PpapiHostMsg_PPBGraphics3D_DestroyTransferBuffer(
       ppapi::API_ID_PPB_GRAPHICS_3D, resource_, id));
 }
 
@@ skipping 73 matching lines @@
       last_state_ = state;
     }
   } else {
     last_state_.error = gpu::error::kLostContext;
     ++last_state_.generation;
   }
 }
 
 }  // namespace proxy
 }  // namespace ppapi