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 800afa7bd6d458480f80980816f70d49cca56e56..2c79f71c00e89cde1aa2a58b11afaf2911d0427b 100644
--- a/mojo/aura/context_factory_mojo.h
+++ b/mojo/aura/context_factory_mojo.h
@@ -29,8 +29,11 @@ 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);
 };