Adds output audio volume to iOS logs

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

Index: webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm
diff --git a/webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm b/webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm
index b17c601270c09bb9703de7c3002c9391692c1ff3..87fa5b6cdd3dae8762822702f480c831353dcfc9 100644
--- a/webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm
+++ b/webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm
@@ -101,12 +101,13 @@ NSInteger const kRTCAudioSessionErrorConfiguration = -2;
        "  inputNumberOfChannels: %ld\n"
        "  outputLatency: %f\n"
        "  inputLatency: %f\n"
+       "  outputVolume: %f\n"
        "}";
   NSString *description = [NSString stringWithFormat:format,
       self.category, (long)self.categoryOptions, self.mode,
       self.isActive, self.sampleRate, self.IOBufferDuration,
       self.outputNumberOfChannels, self.inputNumberOfChannels,
-      self.outputLatency, self.inputLatency];
+      self.outputLatency, self.inputLatency, self.outputVolume];
   return description;
 }