chromeos: Look for "Master" or "Digital" mixer elements.

chrome/browser/chromeos/audio_mixer_alsa.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_
 #define CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_
 #pragma once
 
 #include <string>
-#include <vector>
 
 #include "base/basictypes.h"
 #include "base/callback_old.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread.h"
 #include "chrome/browser/chromeos/audio_mixer.h"
 
 class PrefService;
@@ skipping 74 matching lines @@
 
   // Most recently requested muting state.
   bool is_muted_;
 
   // Is there already a pending call to ApplyState() scheduled on |thread_|?
   bool apply_is_pending_;
 
   // Connection to ALSA.  NULL if not connected.
   _snd_mixer* alsa_mixer_;
 
-  // Master mixers (some hardware has e.g. separate headphone and speaker
-  // elements).
-  std::vector<_snd_mixer_elem*> master_elements_;
+  // Master mixer.
+  _snd_mixer_elem* master_element_;
 
   // PCM mixer.  May be NULL if the driver doesn't expose one.
   _snd_mixer_elem* pcm_element_;
 
   PrefService* prefs_;
 
   // Signalled after Disconnect() finishes (which is itself invoked by the
   // d'tor).
   base::WaitableEvent disconnected_event_;
 
   // Background thread used for interacting with ALSA.
   scoped_ptr<base::Thread> thread_;
 
   // Number of times that we've attempted to connect to ALSA.  Just used to keep
   // us from spamming the logs.
   int num_connection_attempts_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioMixerAlsa);
 };
 
 }  // namespace chromeos
 
 DISABLE_RUNNABLE_METHOD_REFCOUNT(chromeos::AudioMixerAlsa);
 
 #endif  // CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_