Use RTCAudioSessionDelegate in AudioDeviceIOS.

webrtc/modules/audio_device/ios/objc/RTCAudioSession.h

 /*
  *  Copyright 2016 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.
  */
 
@@ skipping 104 matching lines @@
 @property(readonly) NSInteger inputNumberOfChannels;
 @property(readonly) NSInteger outputNumberOfChannels;
 @property(readonly) float outputVolume;
 @property(readonly) NSTimeInterval inputLatency;
 @property(readonly) NSTimeInterval outputLatency;
 @property(readonly) NSTimeInterval IOBufferDuration;
 
 /** Default constructor. Do not call init. */
 + (instancetype)sharedInstance;
 
-/** Adds a delegate, which is held weakly. Even though it's held weakly, callers
- *  should still call |removeDelegate| when it's no longer required to ensure
- *  proper dealloc. This is due to internal use of an NSHashTable.
- */
+/** Adds a delegate, which is held weakly. */
 - (void)addDelegate:(id<RTCAudioSessionDelegate>)delegate;
 /** Removes an added delegate. */
 - (void)removeDelegate:(id<RTCAudioSessionDelegate>)delegate;
 
 /** Request exclusive access to the audio session for configuration. This call
  *  will block if the lock is held by another object.
  */
 - (void)lockForConfiguration;
 /** Relinquishes exclusive access to the audio session. */
 - (void)unlockForConfiguration;
@@ skipping 48 matching lines @@
 
 /** Configure the audio session for WebRTC. On failure, we will attempt to
  *  restore the previously used audio session configuration.
  *  |lockForConfiguration| must be called first.
  */
 - (BOOL)configureWebRTCSession:(NSError **)outError;
 
 @end
 
 NS_ASSUME_NONNULL_END