Avoid destroying surface before the parent surface stops referencing it.

mojo/aura/context_factory_mojo.h

Index: mojo/aura/context_factory_mojo.h
diff --git a/mojo/aura/context_factory_mojo.h b/mojo/aura/context_factory_mojo.h
index 437359dd4d894cf5fd207063ee8cf2775a1f4abc..0ea2fe3bd4cdf9f3426f85980b95ecf7050fb3b6 100644
--- a/mojo/aura/context_factory_mojo.h
+++ b/mojo/aura/context_factory_mojo.h
@@ -30,8 +30,11 @@ class ContextFactoryMojo : public ui::ContextFactory {
   virtual bool DoesCreateTestContexts() override;
   virtual cc::SharedBitmapManager* GetSharedBitmapManager() override;
   virtual base::MessageLoopProxy* GetCompositorMessageLoop() override;
+  virtual scoped_ptr<cc::SurfaceIdAllocator> CreateSurfaceIdAllocator()
+      override;
 
   scoped_ptr<cc::SharedBitmapManager> shared_bitmap_manager_;
+  uint32_t next_surface_id_namespace_;
 
   DISALLOW_COPY_AND_ASSIGN(ContextFactoryMojo);
 };