MacViews: UnhandledKeyboardEventHandler stub

ui/views/controls/webview/webview.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 15 matching lines @@
         '../../views.gyp:views',
       ],
       'defines': [
         'WEBVIEW_IMPLEMENTATION',
       ],
       'sources': [
         # Note: file list duplicated in GN build.
         'unhandled_keyboard_event_handler.cc',
         'unhandled_keyboard_event_handler.h',
         'unhandled_keyboard_event_handler_linux.cc',
+        'unhandled_keyboard_event_handler_mac.mm',
         'unhandled_keyboard_event_handler_win.cc',
         'web_dialog_view.cc',
         'web_dialog_view.h',
         'webview.cc',
         'webview.h',
         'webview_export.h',
       ],
     },
   ],
 }