Provide isAudioEnabled flag to control audio unit.

webrtc/modules/audio_device/ios/audio_session_observer.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 10 matching lines @@
  public:
   // Called when audio session interruption begins.
   virtual void OnInterruptionBegin() = 0;
 
   // Called when audio session interruption ends.
   virtual void OnInterruptionEnd() = 0;
 
   // Called when audio route changes.
   virtual void OnValidRouteChange() = 0;
 
-  // Called when audio session has been configured for WebRTC.
-  virtual void OnConfiguredForWebRTC() = 0;
+  // Called when the ability to play or record changes.
+  virtual void OnCanPlayOrRecordChange(bool can_play_or_record) = 0;
 
  protected:
   virtual ~AudioSessionObserver() {}
 };
 
 }  // namespace webrtc
 
 #endif  //  WEBRTC_MODULES_AUDIO_DEVICE_IOS_AUDIO_SESSION_OBSERVER_H_