Use mojo volume interfaces for mash and classic ash.

chrome/browser/chromeos/extensions/extension_system_event_observer.cc

 // Copyright 2013 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.
 
 #include "chrome/browser/chromeos/extensions/extension_system_event_observer.h"
 
 #include "chrome/browser/extensions/api/system_private/system_private_api.h"
+#include "chromeos/audio/cras_audio_handler.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 
 namespace chromeos {
 
 ExtensionSystemEventObserver::ExtensionSystemEventObserver() {
   DBusThreadManager::Get()->GetPowerManagerClient()->AddObserver(this);
   DBusThreadManager::Get()->GetSessionManagerClient()->AddObserver(this);
+  CrasAudioHandler::Get()->AddAudioObserver(this);
 }
 
 ExtensionSystemEventObserver::~ExtensionSystemEventObserver() {
   DBusThreadManager::Get()->GetPowerManagerClient()->RemoveObserver(this);
   DBusThreadManager::Get()->GetSessionManagerClient()->RemoveObserver(this);
+  if (CrasAudioHandler::IsInitialized())
+    CrasAudioHandler::Get()->RemoveAudioObserver(this);
 }
 
 void ExtensionSystemEventObserver::BrightnessChanged(int level,
                                                      bool user_initiated) {
   extensions::DispatchBrightnessChangedEvent(level, user_initiated);
 }
 
 void ExtensionSystemEventObserver::SuspendDone(
     const base::TimeDelta& sleep_duration) {
   extensions::DispatchWokeUpEvent();
 }
 
 void ExtensionSystemEventObserver::ScreenIsUnlocked() {
   extensions::DispatchScreenUnlockedEvent();
 }
 
+void ExtensionSystemEventObserver::OnOutputNodeVolumeChanged(uint64_t node_id,
+                                                             int volume) {
+  CrasAudioHandler* audio_handler = CrasAudioHandler::Get();
+  extensions::DispatchVolumeChangedEvent(
+      audio_handler->GetOutputVolumePercent(), audio_handler->IsOutputMuted());
+}
+
+void ExtensionSystemEventObserver::OnOutputMuteChanged(
+    bool /* mute_on */,
+    bool /* system_adjust */) {
+  CrasAudioHandler* audio_handler = CrasAudioHandler::Get();

[sky, 2016/10/20 15:41:07]

This is the same as OnOutputMuteChanged. Move to common function, perhaps
DispatchVolumeChangedEvent()?

[msw, 2016/10/20 16:15:32]

Done.

+  extensions::DispatchVolumeChangedEvent(
+      audio_handler->GetOutputVolumePercent(), audio_handler->IsOutputMuted());
+}
+
 }  // namespace chromeos