Get rid of the EnableClose() infrastructure in Widget.

ui/views/widget/native_widget_win.cc

Index: ui/views/widget/native_widget_win.cc
===================================================================
--- ui/views/widget/native_widget_win.cc	(revision 111086)
+++ ui/views/widget/native_widget_win.cc	(working copy)
@@ -756,13 +756,6 @@
     DestroyWindow(hwnd());
 }
 
-void NativeWidgetWin::EnableClose(bool enable) {
-  // Disable the native frame's close button regardless of whether or not the
-  // native frame is in use, since this also affects the system menu.
-  EnableMenuItem(GetSystemMenu(GetNativeView(), false), SC_CLOSE, enable);
-  SendFrameChanged(GetNativeView());
-}
-
 void NativeWidgetWin::Show() {
   if (!IsWindow())
     return;