views: Add OnEnabledChanged() method to View class.

views/view.h

Index: views/view.h
diff --git a/views/view.h b/views/view.h
index 25b6e0f34d7d21390ded808f9f7c471f35cc3ccd..55a5c3dbcc76202dc9a88e6f8ccfd3f7540179c0 100644
--- a/views/view.h
+++ b/views/view.h
@@ -317,7 +317,7 @@ class View : public AcceleratorTarget {
   // Set whether this view is enabled. A disabled view does not receive keyboard
   // or mouse inputs. If flag differs from the current value, SchedulePaint is
   // invoked.
-  virtual void SetEnabled(bool flag);
+  void SetEnabled(bool enabled);
 
   // Returns whether the view is enabled.
   virtual bool IsEnabled() const;
@@ -938,6 +938,10 @@ class View : public AcceleratorTarget {
   // its ancestors. This is used for clipping NativeViewHost.
   virtual void OnVisibleBoundsChanged();
 
+  // Override to be notified when the enabled state of this View has
+  // changed. The default implementation calls SchedulePaint() on this View.
+  virtual void OnEnabledChanged();
+
   // TODO(beng): eliminate in protected.
   // Whether this view is enabled.
   bool enabled_;