Refactor the TrayAudio code so that it can be used by other platforms.

chrome/browser/ui/ash/system_tray_delegate_chromeos.cc

Index: chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
diff --git a/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc b/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
index d28de2cdea5c14b194adb08ad9ce6b4d6c2ed509..1b5784d8cc775308b82b53d47a0c3d4a87eb2bd0 100644
--- a/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
+++ b/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
@@ -311,6 +311,9 @@ void SystemTrayDelegateChromeOS::Initialize() {
 
   if (LoginState::IsInitialized())
     LoginState::Get()->AddObserver(this);
+
+  if (CrasAudioHandler::IsInitialized())
+    CrasAudioHandler::Get()->AddAudioObserver(this);
 }
 
 void SystemTrayDelegateChromeOS::Shutdown() {
@@ -365,7 +368,10 @@ SystemTrayDelegateChromeOS::~SystemTrayDelegateChromeOS() {
       ->RemoveSessionStateObserver(this);
   LoginState::Get()->RemoveObserver(this);
 
-  // Stop observing Drive operations.
+  if (CrasAudioHandler::IsInitialized())
+    CrasAudioHandler::Get()->RemoveAudioObserver(this);
+
+// Stop observing Drive operations.
   UnobserveDriveUpdates();
 
   policy::BrowserPolicyConnectorChromeOS* connector =
@@ -1206,6 +1212,33 @@ void SystemTrayDelegateChromeOS::InputMethodPropertyChanged(
   GetSystemTrayNotifier()->NotifyRefreshIME(false);
 }
 
+// Overridden from CrasAudioHandler::AudioObserver.
+void SystemTrayDelegateChromeOS::OnOutputVolumeChanged() {
+  GetSystemTrayNotifier()->NotifyAudioOutputVolumeChanged();
+}
+
+void SystemTrayDelegateChromeOS::OnOutputMuteChanged() {
+  GetSystemTrayNotifier()->NotifyAudioOutputMuteChanged();
+}
+
+void SystemTrayDelegateChromeOS::OnInputGainChanged() {
+}
+
+void SystemTrayDelegateChromeOS::OnInputMuteChanged() {
+}
+
+void SystemTrayDelegateChromeOS::OnAudioNodesChanged() {
+  GetSystemTrayNotifier()->NotifyAudioNodesChanged();
+}
+
+void SystemTrayDelegateChromeOS::OnActiveOutputNodeChanged() {
+  GetSystemTrayNotifier()->NotifyAudioActiveOutputNodeChanged();
+}
+
+void SystemTrayDelegateChromeOS::OnActiveInputNodeChanged() {
+  GetSystemTrayNotifier()->NotifyAudioActiveInputNodeChanged();
+}
+
 // drive::JobListObserver overrides.
 void SystemTrayDelegateChromeOS::OnJobAdded(const drive::JobInfo& job_info) {
   OnJobUpdated(job_info);