Set up hdmi output device default volume to 100.

chromeos/audio/audio_devices_pref_handler.h

Index: chromeos/audio/audio_devices_pref_handler.h
diff --git a/chromeos/audio/audio_devices_pref_handler.h b/chromeos/audio/audio_devices_pref_handler.h
index d382218d91118c358cc8255040447886d1cddc92..417c4ecbb8a4ea80417c5eb09a1098dd38c53c00 100644
--- a/chromeos/audio/audio_devices_pref_handler.h
+++ b/chromeos/audio/audio_devices_pref_handler.h
@@ -25,7 +25,8 @@ class CHROMEOS_EXPORT AudioDevicesPrefHandler
   // Gets the audio output volume value from prefs for a device. Since we can
   // only have either a gain or a volume for a device (depending on whether it
   // is input or output), we don't really care which value it is.
-  virtual double GetVolumeGainValue(const AudioDevice& device) = 0;
+  virtual double GetOutputVolumeValue(const AudioDevice* device) = 0;
+  virtual double GetInputGainValue(const AudioDevice* device) = 0;
   // Sets the audio volume or gain value to prefs for a device.
   virtual void SetVolumeGainValue(const AudioDevice& device, double value) = 0;