Add notification (and unit test) for closing prefs window so it can be cleane...

chrome/browser/cocoa/preferences_window_controller.h

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <Cocoa/Cocoa.h>
 
 class PrefService;
 
 // A window controller that handles the preferences window.
 @interface PreferencesWindowController : NSWindowController {
  @private
   PrefService* prefs_;  // weak ref
 }
 
 // Designated initializer. |prefs| should not be NULL.
 - (id)initWithPrefs:(PrefService*)prefs;
 
 // Show the preferences window.
 - (IBAction)showPreferences:(id)sender;
 
 @end
+
+// NSNotification sent when the prefs window is closed.
+extern NSString* const kUserDoneEditingPrefsNotification;