Improved error handling in iOS ADM to avoid race during init

webrtc/modules/audio_device/ios/audio_device_ios.h

Index: webrtc/modules/audio_device/ios/audio_device_ios.h
diff --git a/webrtc/modules/audio_device/ios/audio_device_ios.h b/webrtc/modules/audio_device/ios/audio_device_ios.h
index 8f8ba0a9c53ce7c6cd059885f3e241829bf01dea..c4eb0d6f6451a5e8b8efa8da3924eb0236cc26bd 100644
--- a/webrtc/modules/audio_device/ios/audio_device_ios.h
+++ b/webrtc/modules/audio_device/ios/audio_device_ios.h
@@ -182,7 +182,10 @@ class AudioDeviceIOS : public AudioDeviceGeneric {
   bool InitPlayOrRecord();
 
   // Closes and deletes the voice-processing I/O unit.
-  bool ShutdownPlayOrRecord();
+  void ShutdownPlayOrRecord();
+
+  // Helper method for destroying the existing audio unit.
+  void DisposeAudioUnit();
 
   // Callback function called on a real-time priority I/O thread from the audio
   // unit. This method is used to signal that recorded audio is available.