Disable app_shell_unittests on the mac GN builds for now.

BUILD.gn

 # Copyright (c) 2013 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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 126 matching lines @@
     "//ui/surface",
     "//ui/touch_selection",
     "//ui/views",
     "//ui/views/controls/webview",
     "//ui/web_dialogs",
     "//url",
     "//v8:v8",
   ]
   deps += root_extra_deps
 
-  if (enable_extensions) {
+  # TODO(GYP): Get this working on the mac?
+  if (enable_extensions && !is_mac) {
     deps += [ "//extensions/shell:app_shell_unittests" ]
   }
 
   if (!is_win) {
     deps += [ "//breakpad:symupload" ]
   }
 
   if (is_linux) {
     deps += [
       "//dbus",
@@ skipping 150 matching lines @@
       "//ui/views",
       "//ui/views/controls/webview",
       "//ui/web_dialogs",
     ]
   }
 
   if (is_mac || is_ios) {
     deps -= [ "//ui/touch_selection" ]
   }
 }