Abstract notification clicks in its own dictionary

chrome/browser/ui/cocoa/notifications/BUILD.gn

 # Copyright 2016 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.
 
 static_library("common") {
   sources = [
     "notification_builder_mac.h",
     "notification_builder_mac.mm",
+    "notification_constants_mac.h",
+    "notification_constants_mac.mm",
+    "notification_response_builder_mac.h",
+    "notification_response_builder_mac.mm",
   ]
 
   deps = [
     "//base",
     "//chrome:strings",
     "//ui/base:base",
   ]
 }