Adds code to isolate use-after-free in Views

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 c1d69f92cc313e4d73fdb4b6b1124a54ef588e50..2c74338872e1b68ea1d3a13c8b7746679b62bfc4 100644
--- a/ui/views/view_observer.h
+++ b/ui/views/view_observer.h
@@ -33,6 +33,9 @@ class VIEWS_EXPORT ViewObserver {
   // parent view. |view| is the child view being moved.
   virtual void OnChildViewReordered(View* view) {}
 
+  // Called from ~View.
+  virtual void OnViewIsDeleting(View* view) {}
+
  protected:
   virtual ~ViewObserver() {}
 };