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

ui/ozone/public/surface_factory_ozone.h

 // Copyright (c) 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.
 
 #ifndef UI_OZONE_PUBLIC_SURFACE_FACTORY_OZONE_H_
 #define UI_OZONE_PUBLIC_SURFACE_FACTORY_OZONE_H_
 
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/native_library.h"
+#include "base/threading/thread_checker.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/overlay_transform.h"
 #include "ui/ozone/ozone_base_export.h"
 
 class SkBitmap;
 class SkCanvas;
 
@@ skipping 139 matching lines @@
   // Returns true if overlays can be shown at z-index 0, replacing the main
   // surface. Combined with surfaceless extensions, it allows for an
   // overlay-only mode.
   virtual bool CanShowPrimaryPlaneAsOverlay();
 
   // Returns true if the platform is able to create buffers for a specific usage
   // such as MAP for zero copy or SCANOUT for display controller.
   virtual bool CanCreateNativePixmap(BufferUsage usage);
 
  private:
+  base::ThreadChecker thread_checker_;

[reveman, 2015/04/01 19:22:20]

A thread checker is good but please move it to the implementation instead of the
interface.

[dshwang, 2015/04/02 07:56:05]

This thread check is added to check SurfaceFactoryOzone::GetInstance() which is
implemented in this class, instead of subclass.
If moving thread check to subclass, I think there is no way to check
SurfaceFactoryOzone::GetInstance() 

[reveman, 2015/04/02 12:35:39]

GetInstance() is static. The thread usage restriction is a restriction of the
implementation of this interface, not the interface itself.

In general, it's nice to keep this as an interface because it allows an
implementation to cleanly implement not just this interface. When you add a
member here it becomes more of a base class and I would expect a "is-a"
relationship between this class and a derived class.

[dshwang, 2015/04/02 14:26:27]

Alright, I move thread check to each implementation.

   static SurfaceFactoryOzone* impl_;  // not owned
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PUBLIC_SURFACE_FACTORY_OZONE_H_