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

cc/resources/single_release_callback.h

 // Copyright 2013 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_SINGLE_RELEASE_CALLBACK_H_
 #define CC_RESOURCES_SINGLE_RELEASE_CALLBACK_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
 #include "cc/resources/release_callback.h"
 
 namespace cc {
 
 class CC_EXPORT SingleReleaseCallback {
  public:
   static scoped_ptr<SingleReleaseCallback> Create(const ReleaseCallback& cb) {
     return make_scoped_ptr(new SingleReleaseCallback(cb));
   }
 
   ~SingleReleaseCallback();
 
-  void Run(unsigned sync_point, bool is_lost);
+  void Run(uint32 sync_point, bool is_lost);
 
  private:
   explicit SingleReleaseCallback(const ReleaseCallback& callback);
 
   bool has_been_run_;
   ReleaseCallback callback_;
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_SINGLE_RELEASE_CALLBACK_H_