[Mac] Move UI item validation to UserInterfaceItemCommandHandler.

chrome/browser/ui/cocoa/chrome_command_dispatcher_delegate.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_CHROME_COMMAND_DISPATCHER_DELEGATE_H_
 #define CHROME_BROWSER_UI_COCOA_CHROME_COMMAND_DISPATCHER_DELEGATE_H_
 
 #import <Cocoa/Cocoa.h>
 
 #import "ui/base/cocoa/command_dispatcher.h"
 
 // Implement CommandDispatcherDelegate by intercepting browser window keyboard
-// shortcuts and executing them with chrome::ExecuteCommand.
-@interface ChromeCommandDispatcherDelegate : NSObject<CommandDispatcherDelegate>
+// shortcuts and executing them with chrome::ExecuteCommand. Implement
+// UserInterfaceItemCommandHandler by validating items using global chrome::
+// functions and executing commands with chrome::ExecuteCommand().
+@interface ChromeCommandDispatcherDelegate
+    : NSObject<CommandDispatcherDelegate, UserInterfaceItemCommandHandler>
 
 // Checks if |event| is a keyboard shortcut listed in
 // global_keyboard_shortcuts_mac.h. If so, execute the associated command.
 // Returns YES if the event was handled.
 - (BOOL)handleExtraKeyboardShortcut:(NSEvent*)event window:(NSWindow*)window;
 
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_CHROME_COMMAND_DISPATCHER_DELEGATE_H_