[GN Build] Add a dependency on //third_party/mozilla to //ui/base on Mac.

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")
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
@@ skipping 510 matching lines @@
     if (!use_aura) {
       sources -= [
         "view_prop.cc",
         "view_prop.h",
       ]
     }
   }
 
   if (is_mac) {
     deps += [
-      #TODO(tfarina): port this third_party component to GN.
-      #"//third_party/mozilla",
+      "//third_party/mozilla",
     ]
 
     sources -= [
       "cursor/image_cursors.cc",
       "cursor/image_cursors.h",
       "dragdrop/drag_utils.cc",
       "dragdrop/drag_utils.h",
     ]
 
     libs += [
@@ skipping 353 matching lines @@
     deps += [
       "//ui/aura:test_support",
       "//ui/events:gesture_detection",
       #'../chromeos/chromeos.gyp:chromeos',  TODO(GYP)
       #'chromeos/ui_chromeos.gyp:ui_chromeos',
     ]
   }
 }
 }
 # TODO(GYP) Mac (ui_unittest_bundle) and Android (ui_unittests_apk).