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

gpu/command_buffer/common/mailbox.h

Index: gpu/command_buffer/common/mailbox.h
diff --git a/gpu/command_buffer/common/mailbox.h b/gpu/command_buffer/common/mailbox.h
index 938167f5cf8142b078cd32af506f1d10b4d384f9..975d186d5123b0e910a950550fa8137d54f83412 100644
--- a/gpu/command_buffer/common/mailbox.h
+++ b/gpu/command_buffer/common/mailbox.h
@@ -7,6 +7,8 @@
 
 #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"
 
@@ -23,6 +25,18 @@ struct GPU_EXPORT Mailbox {
   }
 };
 
+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_