gpu: Use a local int to generate the gmb id.

content/common/generic_shared_memory_id_generator.cc

-// Copyright 2015 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 "content/common/generic_shared_memory_id_generator.h"
-
-#include "base/atomic_sequence_num.h"
-
-namespace content {
-namespace {
-
-// Global atomic to generate gpu memory buffer unique IDs.
-base::StaticAtomicSequenceNumber g_next_generic_shared_memory_id;
-
-}  // namespace
-
-gfx::GenericSharedMemoryId GetNextGenericSharedMemoryId() {
-  return gfx::GenericSharedMemoryId(g_next_generic_shared_memory_id.GetNext());
-}
-
-}  // namespace content