mac/gn: Add tests to media_unittests missing in gn build.

media/base/mac/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.
 
 assert(is_mac || is_ios)
 
 source_set("mac") {
   # Note: This source_set is depended on only by //media. In the component
   # build, if other component targets also depend on it, multiple copies of
   # the ObjC classes declared in the files below will cause warnings at
@@ skipping 27 matching lines @@
     "//media:media_config",
     "//media:media_implementation",
   ]
 }
 
 source_set("unittests") {
   testonly = true
   sources = [
     "video_frame_mac_unittests.cc",
   ]
+  libs = [ "CoreVideo.framework" ]
   configs += [ "//media:media_config" ]
   deps = [
     "//testing/gtest",
   ]
 }