Fix the volume controlling behaviors.

chrome/browser/chromeos/audio/audio_handler.cc

Index: chrome/browser/chromeos/audio/audio_handler.cc
diff --git a/chrome/browser/chromeos/audio/audio_handler.cc b/chrome/browser/chromeos/audio/audio_handler.cc
index fc4316294856cd3cb0be3743980e9e9aedff8dda..13606a23a2e4281955a55b8e9a1637eddb8fb31c 100644
--- a/chrome/browser/chromeos/audio/audio_handler.cc
+++ b/chrome/browser/chromeos/audio/audio_handler.cc
@@ -40,7 +40,11 @@ static AudioHandler* g_audio_handler = NULL;
 // static
 void AudioHandler::Initialize() {
   CHECK(!g_audio_handler);
-  g_audio_handler = new AudioHandler();
+#if defined(USE_CRAS)
+  g_audio_handler = new AudioHandler(new AudioMixerCras());
+#else
+  g_audio_handler = new AudioHandler(new AudioMixerAlsa());
+#endif
 }
 
 // static
@@ -53,6 +57,12 @@ void AudioHandler::Shutdown() {
 }
 
 // static
+void AudioHandler::InitializeForTesting(AudioMixer* mixer) {
+  CHECK(!g_audio_handler);
+  g_audio_handler = new AudioHandler(mixer);
+}
+
+// static
 AudioHandler* AudioHandler::GetInstance() {
   VLOG_IF(1, !g_audio_handler)
       << "AudioHandler::GetInstance() called with NULL global instance.";
@@ -113,12 +123,8 @@ void AudioHandler::RemoveVolumeObserver(VolumeObserver* observer) {
   volume_observers_.RemoveObserver(observer);
 }
 
-AudioHandler::AudioHandler()
-#if defined(USE_CRAS)
-    : mixer_(new AudioMixerCras()),
-#else
-    : mixer_(new AudioMixerAlsa()),
-#endif
+AudioHandler::AudioHandler(AudioMixer* mixer)
+    : mixer_(mixer),
       prefs_(g_browser_process->local_state()) {
   mixer_->SetVolumePercent(prefs_->GetDouble(prefs::kAudioVolumePercent));
   mixer_->SetMuted(prefs_->GetInteger(prefs::kAudioMute) == kPrefMuteOn);