Refactor AudioUnit code into its own class.

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

 /*
  *  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 57 matching lines @@
                    name:AVAudioSessionMediaServicesWereResetNotification
                  object:nil];
   }
   return self;
 }
 
 - (void)dealloc {
   [[NSNotificationCenter defaultCenter] removeObserver:self];
 }
 
+- (NSString *)description {
+  NSString *format =
+      @"RTCAudioSession: {\n"
+       "  isActive: %d\n"
+       "  sampleRate: %.2f\n"
+       "  IOBufferDuration: %f\n"
+       "  outputNumberOfChannels: %ld\n"
+       "  inputNumberOfChannels: %ld\n"
+       "  outputLatency: %f\n"
+       "  inputLatency: %f\n"
+       "}";
+  NSString *description = [NSString stringWithFormat:format,
+      self.isActive, self.sampleRate, self.IOBufferDuration,
+      self.outputNumberOfChannels, self.inputNumberOfChannels,
+      self.outputLatency, self.inputLatency];
+  return description;
+}
+
 - (void)setIsActive:(BOOL)isActive {
   @synchronized(self) {
     _isActive = isActive;
   }
 }
 
 - (BOOL)isActive {
   @synchronized(self) {
     return _isActive;
   }
@@ skipping 483 matching lines @@
   }
 }
 
 - (void)notifyMediaServicesWereReset {
   for (auto delegate : self.delegates) {
     [delegate audioSessionMediaServicesWereReset:self];
   }
 }
 
 @end