Get rid of the EnableClose() infrastructure in Widget.

ui/views/widget/widget.h

Index: ui/views/widget/widget.h
===================================================================
--- ui/views/widget/widget.h	(revision 111086)
+++ ui/views/widget/widget.h	(working copy)
@@ -321,10 +321,6 @@
   // any code that expects it to be valid beyond this call.
   void CloseNow();
 
-  // Toggles the enable state for the Close button (and the Close menu item in
-  // the system menu).
-  void EnableClose(bool enable);
-
   // Shows or hides the widget, without changing activation state.
   virtual void Show();
   void Hide();