Implement two new policies to control muting the audio I/O.

chrome/browser/chromeos/audio/audio_mixer_alsa.h

Index: chrome/browser/chromeos/audio/audio_mixer_alsa.h
diff --git a/chrome/browser/chromeos/audio/audio_mixer_alsa.h b/chrome/browser/chromeos/audio/audio_mixer_alsa.h
index 215e86fcde181664bd73e1dc126d2bb80f6491c0..e532ae25e0e437ca2ea965099b52a51ebc2fa31c 100644
--- a/chrome/browser/chromeos/audio/audio_mixer_alsa.h
+++ b/chrome/browser/chromeos/audio/audio_mixer_alsa.h
@@ -33,6 +33,12 @@ class AudioMixerAlsa : public AudioMixer {
   virtual void SetVolumePercent(double percent) OVERRIDE;
   virtual bool IsMuted() OVERRIDE;
   virtual void SetMuted(bool muted) OVERRIDE;
+  virtual bool IsMuteLocked() OVERRIDE;
+  virtual void SetMuteLocked(bool locked) OVERRIDE;
+  virtual bool IsCaptureMuted() OVERRIDE;
+  virtual void SetCaptureMuted(bool mute) OVERRIDE;
+  virtual bool IsCaptureMuteLocked() OVERRIDE;
+  virtual void SetCaptureMuteLocked(bool locked) OVERRIDE;
 
  private:
   // Tries to connect to ALSA.  On failure, posts a delayed Connect() task to
@@ -75,7 +81,7 @@ class AudioMixerAlsa : public AudioMixer {
   double DbToPercent(double db) const;
   double PercentToDb(double percent) const;
 
-  // Guards |min_volume_db_|, |max_volume_db_|, |volume_db_|, |is_muted_|,
+  // Guards |min_volume_db_|, |max_volume_db_|, |volume_db_|, the mute state,

[Mattias Nissler (ping if slow), 2012/08/28 12:24:24]

I'd just list the additional members for clarity.

[pastarmovj, 2012/08/28 15:11:50]

Done.

   // |apply_is_pending_|, and |initial_volume_percent_|.
   base::Lock lock_;
 
@@ -88,8 +94,13 @@ class AudioMixerAlsa : public AudioMixer {
   // volume is updated later on |thread_| by ApplyState().
   double volume_db_;
 
-  // Most recently-requested muting state.
+  // Most recently-requested muting state. We don't have control over ALSA so
+  // other sound clients might unmute channels but we can do best effort to
+  // mimic CRASes locking functionality.

[Daniel Erat, 2012/08/27 17:38:35]

nit: s/CRASes/CRAS's/

[pastarmovj, 2012/08/28 15:11:50]

Done.

   bool is_muted_;
+  bool is_mute_locked_;

[Daniel Erat, 2012/08/27 17:38:35]

nit: move is_mute_locked_ and is_capture_mute_locked_ together and add a comment
describing that when they're true, the state of is_muted_ and is_capture_muted_
can't be changed

[pastarmovj, 2012/08/28 15:11:50]

Done.

+  bool is_capture_muted_;
+  bool is_capture_mute_locked_;
 
   // Is there already a pending call to ApplyState() scheduled on |thread_|?
   bool apply_is_pending_;
@@ -109,6 +120,10 @@ class AudioMixerAlsa : public AudioMixer {
   // PCM mixer.  May be NULL if the driver doesn't expose one.
   _snd_mixer_elem* pcm_element_;
 
+  // Mic mixers.  Used to mute capture. Both might be NULL on some drivers.

[Mattias Nissler (ping if slow), 2012/08/28 12:24:24]

nit: Two spaces after period seems to be the rule int this file.

[pastarmovj, 2012/08/28 15:11:50]

Done.

+  _snd_mixer_elem* mic_element_;
+  _snd_mixer_elem* front_mic_element_;
+
   // Signalled after Disconnect() finishes (which is itself invoked by the
   // d'tor).
   base::WaitableEvent disconnected_event_;