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

gpu/command_buffer/common/mailbox_holder.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_holder.h"
+
+namespace gpu {
+
+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