Get rid of the EnableClose() infrastructure in Widget.

chrome/browser/ui/panels/panel_browser_frame_view.cc

Index: chrome/browser/ui/panels/panel_browser_frame_view.cc
===================================================================
--- chrome/browser/ui/panels/panel_browser_frame_view.cc	(revision 111086)
+++ chrome/browser/ui/panels/panel_browser_frame_view.cc	(working copy)
@@ -370,10 +370,6 @@
   window_mask->close();
 }
 
-void PanelBrowserFrameView::EnableClose(bool enable) {
-  close_button_->SetEnabled(enable);
-}
-
 void PanelBrowserFrameView::ResetWindowControls() {
   // The close button isn't affected by this constraint.
 }