[Presentation API] Change ListenForSessionMessages API to client-style.

chrome/browser/media/router/media_router.gypi

 # Copyright (c) 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.
 
 {
   'variables': {
     # File lists shared with GN build.
     'media_router_sources': [
       'create_presentation_session_request.cc',
       'create_presentation_session_request.h',
@@ skipping 17 matching lines @@
       'media_sinks_observer.cc',
       'media_sinks_observer.h',
       'media_source.cc',
       'media_source.h',
       'media_source_helper.cc',
       'media_source_helper.h',
       'presentation_media_sinks_observer.cc',
       'presentation_media_sinks_observer.h',
       'presentation_service_delegate_impl.cc',
       'presentation_service_delegate_impl.h',
+      'presentation_session_messages_observer.cc',
+      'presentation_session_messages_observer.h',
       'presentation_session_state_observer.cc',
       'presentation_session_state_observer.h',
     ],
     # Files that are only needed on desktop builds
     'media_router_non_android_sources': [
       'media_router_mojo_impl.cc',
       'media_router_mojo_impl.h',
       'media_router_type_converters.cc',
       'media_router_type_converters.h',
     ],
     'media_router_test_support_sources': [
       'media_router_mojo_test.cc',
       'media_router_mojo_test.h',
       'mock_media_router.cc',
       'mock_media_router.h',
       'mock_screen_availability_listener.cc',
       'mock_screen_availability_listener.h',
       'test_helper.cc',
       'test_helper.h',
     ],
   },
 }