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

gpu/command_buffer/common/mailbox.cc

 // 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.
 
 #include "gpu/command_buffer/common/mailbox.h"
 
 #include <string.h>
 
 #include "base/logging.h"
 
@@ skipping 13 matching lines @@
 
 void Mailbox::SetZero() {
   memset(name, 0, sizeof(name));
 }
 
 void Mailbox::SetName(const int8* n) {
   DCHECK(IsZero() || !memcmp(name, n, sizeof(name)));
   memcpy(name, n, sizeof(name));
 }
 
+MailboxHolder::MailboxHolder() : texture_target(0), sync_point(0) {}
+
+MailboxHolder::MailboxHolder(const Mailbox& mailbox,
+                             uint32 texture_target,
+                             uint32 sync_point)
+    : mailbox(mailbox),
+      texture_target(texture_target),
+      sync_point(sync_point) {}
+
 }  // namespace gpu