[Mac] Support for Touch Bar Customization

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/buildflag_header.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 import("//ui/base/ui_features.gni")
@@ skipping 120 matching lines @@
     "cocoa/nsview_additions.mm",
     "cocoa/remote_layer_api.h",
     "cocoa/remote_layer_api.mm",
     "cocoa/scoped_cg_context_smooth_fonts.h",
     "cocoa/scoped_cg_context_smooth_fonts.mm",
     "cocoa/three_part_image.h",
     "cocoa/three_part_image.mm",
     "cocoa/tool_tip_base_view.h",
     "cocoa/tool_tip_base_view.mm",
     "cocoa/touch_bar_forward_declarations.h",
+    "cocoa/touch_bar_forward_declarations.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",
@@ skipping 838 matching lines @@
 if (is_mac) {
   mac_framework_bundle("ui_unittests_framework") {
     testonly = true
     deps = [
       "//ui/resources:ui_test_pak_bundle_data",
     ]
     info_plist = "test/framework-Info.plist"
     output_name = "ui_unittests Framework"
   }
 }