Get content_unittests to link on the mac GN build.

content/test/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/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/module_args/v8.gni")
 import("//testing/test.gni")
@@ skipping 544 matching lines @@
       "//media:shared_memory_support",
       "//media/audio:test_support",
       "//media/base:test_support",
       "//media/midi:midi",
       "//storage/browser",
       "//storage/common",
       "//third_party/WebKit/public:blink",
       "//third_party/icu",
       "//third_party/leveldatabase",
       "//third_party/libjingle",
+      "//ui/compositor:test_support",
       "//ui/gl",
       "//ui/gl:test_support",
     ]
   }
 
   data_deps = [ "//third_party/mesa:osmesa" ]
 
   if (!is_win) {
     sources += [ "../browser/file_descriptor_info_impl_unittest.cc" ]
   }
@@ skipping 201 matching lines @@
       "//testing/gtest",
       "//third_party/WebKit/public:blink",
       "//ui/base",
       "//ui/gfx",
       "//ui/gfx/geometry",
       "//ui/gl",
       "//ui/gl:test_support",
     ]
   }
 }