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

ui/ozone/platform/drm/drm_surface_factory.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 UI_OZONE_PLATFORM_DRM_DRM_SURFACE_FACTORY_H_
 #define UI_OZONE_PLATFORM_DRM_DRM_SURFACE_FACTORY_H_
 
 #include "base/memory/scoped_ptr.h"
+#include "base/threading/thread_checker.h"
 #include "ui/ozone/public/surface_factory_ozone.h"
 
 namespace ui {
 
 class ScreenManager;
 class SurfaceOzoneCanvas;
 
 // SurfaceFactoryOzone implementation on top of DRM/KMS using dumb buffers.
 // This implementation is used in conjunction with the software rendering
 // path.
 class DrmSurfaceFactory : public SurfaceFactoryOzone {
  public:
   DrmSurfaceFactory(ScreenManager* screen_manager);
   ~DrmSurfaceFactory() override;
 
   // SurfaceFactoryOzone:
   scoped_ptr<SurfaceOzoneCanvas> CreateCanvasForWidget(
       gfx::AcceleratedWidget widget) override;
   bool LoadEGLGLES2Bindings(
       AddGLLibraryCallback add_gl_library,
       SetGLGetProcAddressProcCallback set_gl_get_proc_address) override;
 
  protected:
   ScreenManager* screen_manager_;  // Not owned.
+  base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(DrmSurfaceFactory);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRM_DRM_SURFACE_FACTORY_H_