Add gpu::MailboxHolder to hold state for a gpu::Mailbox

cc/resources/transferable_resource.h

 // Copyright 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 CC_RESOURCES_TRANSFERABLE_RESOURCE_H_
 #define CC_RESOURCES_TRANSFERABLE_RESOURCE_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/resources/resource_format.h"
-#include "gpu/command_buffer/common/mailbox.h"
+#include "gpu/command_buffer/common/mailbox_holder.h"
 #include "ui/gfx/size.h"
 
 namespace cc {
 
 struct ReturnedResource;
 typedef std::vector<ReturnedResource> ReturnedResourceArray;
 struct TransferableResource;
 typedef std::vector<TransferableResource> TransferableResourceArray;
 
 struct CC_EXPORT TransferableResource {
   TransferableResource();
   ~TransferableResource();
 
   ReturnedResource ToReturnedResource() const;
   static void ReturnResources(const TransferableResourceArray& input,
                               ReturnedResourceArray* output);
 
   unsigned id;
-  unsigned sync_point;
   ResourceFormat format;
-  uint32 target;
   uint32 filter;
   gfx::Size size;
-  gpu::Mailbox mailbox;
+  gpu::MailboxHolder mailbox_holder;
   bool is_software;
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_TRANSFERABLE_RESOURCE_H_