Use base::AtomicSequenceNumber for the flush id in GLES2Implementation

gpu/command_buffer/client/gles2_implementation.cc

 // Copyright (c) 2012 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.
 
 // A class to emulate GLES2 over command buffers.
 
 #include "gpu/command_buffer/client/gles2_implementation.h"
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
 #include <GLES2/gl2extchromium.h>
 #include <GLES3/gl3.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <algorithm>
 #include <map>
 #include <set>
 #include <sstream>
 #include <string>
+#include "base/atomic_sequence_num.h"
 #include "base/compiler_specific.h"
 #include "base/strings/string_split.h"
 #include "base/strings/stringprintf.h"
 #include "base/sys_info.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/trace_event/memory_allocator_dump.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "base/trace_event/process_memory_dump.h"
 #include "base/trace_event/trace_event.h"
 #include "gpu/command_buffer/client/buffer_tracker.h"
@@ skipping 40 matching lines @@
     memcpy(dest, source, size);
   }
 }
 
 // A 32-bit and 64-bit compatible way of converting a pointer to a GLuint.
 GLuint ToGLuint(const void* ptr) {
   return static_cast<GLuint>(reinterpret_cast<size_t>(ptr));
 }
 
 uint32_t GenerateNextFlushId() {
-  static base::subtle::Atomic32 flush_id = 0;
-  base::subtle::Atomic32 my_id =
-      base::subtle::Barrier_AtomicIncrement(&flush_id, 1);
-  return static_cast<uint32_t>(my_id);
+  static base::AtomicSequenceNumber flush_id;

[piman, 2016/03/16 23:49:29]

I was thinking, move this out of the function and as a
StaticAtomicSequenceNumber, to avoid the constructor/destructor

[danakj, 2016/03/16 23:50:41]

Oh, snap. Sure :)

+  return static_cast<uint32_t>(flush_id.GetNext());
 }
 
 }  // anonymous namespace
 
 #if !defined(_MSC_VER)
 const size_t GLES2Implementation::kMaxSizeOfSimpleResult;
 const unsigned int GLES2Implementation::kStartingOffset;
 #endif
 
 GLES2Implementation::GLStaticState::GLStaticState() {
@@ skipping 6729 matching lines @@
   cached_extensions_.clear();
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "gpu/command_buffer/client/gles2_implementation_impl_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu