Use RTCAudioSessionDelegate in AudioDeviceIOS.

webrtc/modules/modules.gyp

 # Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 {
   'includes': [
@@ skipping 462 matching lines @@
             }],
             ['OS=="ios"', {
               'includes': [
                 '../build/objc_common.gypi',
               ],
               'sources': [
                 'video_coding/codecs/h264/h264_video_toolbox_nalu_unittest.cc',
                 'audio_device/ios/audio_device_unittest_ios.cc',
                 'audio_device/ios/objc/RTCAudioSessionTest.mm',
               ],
+              'xcode_settings': {
+                'OTHER_LDFLAGS': ['-ObjC'],
+              },
               # This needs to be kept in sync with modules_unittests.isolate.
               'mac_bundle_resources': [
                 '<(DEPTH)/data/audio_processing/output_data_float.pb',
                 '<(DEPTH)/data/audio_processing/output_data_mac.pb',
                 '<(DEPTH)/data/voice_engine/audio_tiny48.wav',
                 '<(DEPTH)/resources/att-downlink.rx',
                 '<(DEPTH)/resources/att-uplink.rx',
                 '<(DEPTH)/resources/audio_coding/neteq4_network_stats.dat',
                 '<(DEPTH)/resources/audio_coding/neteq4_opus_network_stats.dat',
                 '<(DEPTH)/resources/audio_coding/neteq4_opus_ref.pcm',
@@ skipping 210 matching lines @@
               'sources': [
                 'video_render_tests.isolate',
               ],
             },
           ],
         }],
       ],
     }], # include_tests
   ], # conditions
 }