Support delayed AudioUnit initialization.

webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.m

 /*
  *  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 82 matching lines @@
     _inputNumberOfChannels = kRTCAudioSessionPreferredNumberOfChannels;
     _outputNumberOfChannels = kRTCAudioSessionPreferredNumberOfChannels;
   }
   return self;
 }
 
 + (instancetype)currentConfiguration {
   RTCAudioSession *session = [RTCAudioSession sharedInstance];
   RTCAudioSessionConfiguration *config =
       [[RTCAudioSessionConfiguration alloc] init];
+  config.category = session.category;
+  config.categoryOptions = session.categoryOptions;
   config.mode = session.mode;
   config.sampleRate = session.sampleRate;
   config.ioBufferDuration = session.IOBufferDuration;
   config.inputNumberOfChannels = session.inputNumberOfChannels;
   config.outputNumberOfChannels = session.outputNumberOfChannels;
   return config;
 }
 
 + (instancetype)webRTCConfiguration {
   return [[self alloc] init];
 }
 
 @end