Make CompositorObserver’s destructor protected-and-virtual.

ui/compositor/compositor_observer.h

Index: ui/compositor/compositor_observer.h
diff --git a/ui/compositor/compositor_observer.h b/ui/compositor/compositor_observer.h
index d5f3371f5a734a3b1bf4eaf2b087fe46a46c5035..f833a5ae5c12cc8349b8b48193b443f853e2fcb1 100644
--- a/ui/compositor/compositor_observer.h
+++ b/ui/compositor/compositor_observer.h
@@ -38,6 +38,9 @@ class COMPOSITOR_EXPORT CompositorObserver {
   // Called at the top of the compositor's destructor, to give observers a
   // chance to remove themselves.
   virtual void OnCompositingShuttingDown(Compositor* compositor) = 0;
+
+ protected:

[danakj, 2017/03/29 21:35:49]

Can you please make it public though?

+  virtual ~CompositorObserver() {}
 };
 
 }  // namespace ui