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

gpu/command_buffer/common/mailbox.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 GPU_COMMAND_BUFFER_MAILBOX_H_
 #define GPU_COMMAND_BUFFER_MAILBOX_H_
 
 #include <string.h>
 
+#include "base/callback_forward.h"
+#include "base/memory/scoped_ptr.h"
 #include "gpu/command_buffer/common/types.h"
 #include "gpu/gpu_export.h"
 
 namespace gpu {
 
 struct GPU_EXPORT Mailbox {
   Mailbox();
   bool IsZero() const;
   void SetZero();
   void SetName(const int8* name);
   int8 name[64];
   bool operator<(const Mailbox& other) const {
     return memcmp(this, &other, sizeof other) < 0;
   }
 };
 
+struct GPU_EXPORT MailboxHolder {
+  typedef base::Callback<void(scoped_ptr<MailboxHolder>)> ReleaseCallback;
+
+  MailboxHolder();
+  MailboxHolder(const gpu::Mailbox& mailbox,
+                uint32 texture_target,
+                uint32 sync_point);
+  gpu::Mailbox mailbox;
+  uint32 texture_target;
+  uint32 sync_point;
+};
+
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_MAILBOX_H_