zero-copy: Clarify to allocate/destroy GpuMemoryBuffer on any thread and use it on the main thread o

content/common/gpu/gpu_memory_buffer_factory_surface_texture.h

 // Copyright 2014 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.
 
 #ifndef CONTENT_COMMON_GPU_GPU_MEMORY_BUFFER_FACTORY_SURFACE_TEXTURE_H_
 #define CONTENT_COMMON_GPU_GPU_MEMORY_BUFFER_FACTORY_SURFACE_TEXTURE_H_
 
 #include "base/containers/hash_tables.h"
 #include "base/memory/ref_counted.h"
-#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
 #include "content/common/gpu/gpu_memory_buffer_factory.h"
 #include "gpu/command_buffer/service/image_factory.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gpu_memory_buffer.h"
 
 namespace gfx {
 class GLImage;
 class SurfaceTexture;
 }
 
@@ skipping 29 matching lines @@
       const gfx::Size& size,
       gfx::GpuMemoryBuffer::Format format,
       unsigned internalformat,
       int client_id) override;
 
  private:
   typedef std::pair<int, int> SurfaceTextureMapKey;
   typedef base::hash_map<SurfaceTextureMapKey,
                          scoped_refptr<gfx::SurfaceTexture>> SurfaceTextureMap;
   SurfaceTextureMap surface_textures_;
-  base::Lock surface_textures_lock_;
+  base::ThreadChecker thread_checker_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_GPU_GPU_MEMORY_BUFFER_FACTORY_SURFACE_TEXTURE_H_