[Mac] Move UI item validation to UserInterfaceItemCommandHandler.

ui/base/cocoa/user_interface_item_command_handler.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 UI_BASE_COCOA_USER_INTERFACE_ITEM_COMMAND_HANDLER_H_
+#define UI_BASE_COCOA_USER_INTERFACE_ITEM_COMMAND_HANDLER_H_
+
+#import <Cocoa/Cocoa.h>
+
+// Used by CommandDispatchingWindow to implement NSUserInterfaceItemValidations
+// for items with -commandDispatch: and -commandDispatchUsingKeyModifiers:.
+@protocol UserInterfaceItemCommandHandler<NSObject>
+
+// Called by CommandDispatchingWindow to validate menu and toolbar items. All
+// the items we care about have been set with the -commandDispatch or
+// -commandDispatchUsingKeyModifiers selectors and a target of FirstResponder in
+// IB. If it's not one of those, it should be handled elsewhere in the responder
+// chain.
+- (BOOL)validateUserInterfaceItem:(id<NSValidatedUserInterfaceItem>)item
+                           window:(NSWindow*)window;
+
+// Called by CommandDispatchingWindow to execute commands. This assumes that the
+// command is supported and doesn't check, otherwise it would have been disabled
+// in the UI in validateUserInterfaceItem:.
+- (void)commandDispatch:(id)sender window:(NSWindow*)window;
+
+// Same as |-commandDispatch:|, but executes commands using a disposition
+// determined by the key flags. If the window is in the background and the
+// command key is down, ignore the command key, but process any other modifiers.
+- (void)commandDispatchUsingKeyModifiers:(id)sender window:(NSWindow*)window;
+
+@end
+
+#endif  // UI_BASE_COCOA_USER_INTERFACE_ITEM_COMMAND_HANDLER_H_