aura: Support releasing the OutputSurface()

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index 8235c453df32750dc77f1e5265270089c4029c6b..0ba4aea166affba82e222e77c3d375e740987821 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -231,6 +231,10 @@ class COMPOSITOR_EXPORT Compositor
 
   // Sets the widget for the compositor to render into.
   void SetAcceleratedWidget(gfx::AcceleratedWidget widget);
+  // Releases the widget previously set through SetAcceleratedWidget().
+  // After returning it will not be used for rendering anymore.
+  // The compositor must be set to invisible when taking away a widget.
+  gfx::AcceleratedWidget ReleaseAcceleratedWidget();
   gfx::AcceleratedWidget widget() const;
 
   // Returns the vsync manager for this compositor.