[Mac] Move UI item validation to UserInterfaceItemCommandHandler.

ui/base/BUILD.gn

 # Copyright 2014 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("//build/config/ui.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
@@ skipping 69 matching lines @@
     "cocoa/remote_layer_api.h",
     "cocoa/remote_layer_api.mm",
     "cocoa/three_part_image.h",
     "cocoa/three_part_image.mm",
     "cocoa/tool_tip_base_view.h",
     "cocoa/tool_tip_base_view.mm",
     "cocoa/tracking_area.h",
     "cocoa/tracking_area.mm",
     "cocoa/underlay_opengl_hosting_window.h",
     "cocoa/underlay_opengl_hosting_window.mm",
+    "cocoa/user_interface_item_command_handler.h",
     "cocoa/view_description.h",
     "cocoa/view_description.mm",
     "cocoa/window_size_constants.h",
     "cocoa/window_size_constants.mm",
     "cursor/cursor.cc",
     "cursor/cursor.h",
     "cursor/cursor_android.cc",
     "cursor/cursor_loader.h",
     "cursor/cursor_win.cc",
     "default_theme_provider_mac.mm",
@@ skipping 773 matching lines @@
   }
   if (is_mac) {
     data += [ "$root_out_dir/ui_unittests Framework.framework/" ]
 
     if (is_asan && symbol_level == 0) {
       data += [ "$root_out_dir/ui_base_unittests.dSYM/" ]
     }
   }
 }
 # TODO(GYP) Mac (ui_base_tests_bundle)