[Mac/GN] Set up the component 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
+  # run-time.
+  visibility = [ "//media" ]
+
   set_sources_assignment_filter([])
   sources = [
     "coremedia_glue.h",
     "coremedia_glue.mm",
     "corevideo_glue.h",
     "video_frame_mac.cc",
     "video_frame_mac.h",
     "videotoolbox_glue.h",
     "videotoolbox_glue.mm",
     "videotoolbox_helpers.cc",
     "videotoolbox_helpers.h",
   ]
   if (is_mac) {
     sources += [
       "avfoundation_glue.h",
       "avfoundation_glue.mm",
     ]
     libs = [
       "AVFoundation.framework",
-
-      # Required by video_frame_mac.cc.
-      "CoreVideo.framework",
+      "CoreVideo.framework",  # Required by video_frame_mac.cc.
     ]
   }
   set_sources_assignment_filter(sources_assignment_filter)
-  configs += [ "//media:media_config" ]
+  configs += [
+    "//media:media_config",
+    "//media:media_implementation",
+  ]
 }
 
 source_set("unittests") {
   testonly = true
   sources = [
     "video_frame_mac_unittests.cc",
   ]
   configs += [ "//media:media_config" ]
   deps = [
     "//testing/gtest",
   ]
 }