Introduce a type of View background that stays in sync with its host

ui/views/view_observer.h

Index: ui/views/view_observer.h
diff --git a/ui/views/view_observer.h b/ui/views/view_observer.h
index c4f56791d4505e200493b03b7155952276902ca3..9169545d08a173f00423eb92280338e3f8d9647e 100644
--- a/ui/views/view_observer.h
+++ b/ui/views/view_observer.h
@@ -35,6 +35,9 @@ class VIEWS_EXPORT ViewObserver {
   // View::ReorderChildView() is called on |observed_view|.
   virtual void OnChildViewReordered(View* observed_view, View* child) {}
 
+  // FIXME

[msw, 2017/04/14 20:42:17]

FIXME

[Evan Stade, 2017/04/17 15:20:03]

Done.

+  virtual void OnViewNativeThemeChanged(View* observed_view) {}
+
   // Called from ~View.
   virtual void OnViewIsDeleting(View* observed_view) {}