[Media Router] Reland: MediaRouter interfaces with stub implementations.

chrome/browser/media/router/media_router.gyp

 # Copyright 2015 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.
 
 {
   'targets': [
     {
       'target_name': 'media_router',
       'type': 'static_library',
       'include_dirs': [
         '<(DEPTH)',
       ],
       'dependencies': [
         '<(DEPTH)/base/base.gyp:base',
         '<(DEPTH)/url/url.gyp:url_lib',
       ],
       'sources': [
         'common.h',
         'media_route.cc',
         'media_route.h',
         'media_route_id.h',
+        'media_router.h',
+        'media_router_impl.cc',
+        'media_router_impl.h',
+        'media_router_impl_factory.cc',
+        'media_router_impl_factory.h',
+        'media_routes_observer.cc',
+        'media_routes_observer.h',
         'media_sink.cc',
         'media_sink.h',
+        'media_sinks_observer.cc',
+        'media_sinks_observer.h',
         'media_source.cc',
         'media_source.h',
         'media_source_helper.cc',
         'media_source_helper.h',
         'route_id_manager.cc',
         'route_id_manager.h',
       ],
     },
   ],
 }