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

Index: ui/ozone/public/surface_factory_ozone.h
diff --git a/ui/ozone/public/surface_factory_ozone.h b/ui/ozone/public/surface_factory_ozone.h
index 4e223bf1fc8b8abc9252978c29a53e7aaf5179ff..9eb10fffb27b98c6ad53fbc146c6ece3bc957cfd 100644
--- a/ui/ozone/public/surface_factory_ozone.h
+++ b/ui/ozone/public/surface_factory_ozone.h
@@ -8,6 +8,7 @@
 #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"
@@ -167,6 +168,7 @@ class OZONE_BASE_EXPORT SurfaceFactoryOzone {
   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
 };