Supports multiple active input/output audio nodes in CrasAudioHandler.

chromeos/audio/cras_audio_handler.cc

 // Copyright (c) 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 "chromeos/audio/cras_audio_handler.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/bind.h"
@@ skipping 152 matching lines @@
 
 int CrasAudioHandler::GetInputGainPercentForDevice(uint64 device_id) {
   if (device_id == active_input_node_id_) {
     return input_gain_;
   } else {
     const AudioDevice* device = GetDeviceFromId(device_id);
     return static_cast<int>(audio_pref_handler_->GetInputGainValue(device));
   }
 }
 
-uint64 CrasAudioHandler::GetActiveOutputNode() const {
+uint64 CrasAudioHandler::GetPrimaryActiveOutputNode() const {
   return active_output_node_id_;
 }
 
-uint64 CrasAudioHandler::GetActiveInputNode() const {
+uint64 CrasAudioHandler::GetPrimaryActiveInputNode() const {
   return active_input_node_id_;
 }
 
 void CrasAudioHandler::GetAudioDevices(AudioDeviceList* device_list) const {
   device_list->clear();
   for (AudioDeviceMap::const_iterator it = audio_devices_.begin();
        it != audio_devices_.end(); ++it)
     device_list->push_back(it->second);
 }
 
-bool CrasAudioHandler::GetActiveOutputDevice(AudioDevice* device) const {
+bool CrasAudioHandler::GetPrimaryActiveOutputDevice(AudioDevice* device) const {
   const AudioDevice* active_device = GetDeviceFromId(active_output_node_id_);
   if (!active_device || !device)
     return false;
   *device = *active_device;
   return true;
 }
 
 void CrasAudioHandler::SetKeyboardMicActive(bool active) {
   const AudioDevice* keyboard_mic = GetKeyboardMic();
   if (!keyboard_mic)
     return;
-  if (active) {
-    chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->
-        AddActiveInputNode(keyboard_mic->id);
-  } else {
-    chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->
-        RemoveActiveInputNode(keyboard_mic->id);
+  // Keyboard mic is invisible to chromeos users. It is always added or removed
+  // as additional active node.
+  DCHECK(active_input_node_id_ && active_input_node_id_ != keyboard_mic->id);
+  if (active)
+    AddActiveNode(keyboard_mic->id);
+  else
+    RemoveActiveNode(keyboard_mic->id);
+}
+
+void CrasAudioHandler::AddActiveNode(uint64 node_id) {
+  const AudioDevice* device = GetDeviceFromId(node_id);
+  if (!device) {
+    VLOG(1) << "AddActiveInputNode: Cannot find device id="
+            << "0x" << std::hex << node_id;
+    return;
+  }
+
+  // If there is no primary active device, set |node_id| to primary active node.
+  if ((device->is_input && !active_input_node_id_) ||
+      (!device->is_input && !active_output_node_id_)) {
+    SwitchToDevice(*device);
+    return;
+  }
+  AddAdditionalActiveNode(node_id);
+}
+
+void CrasAudioHandler::RemoveActiveNode(uint64 node_id) {
+  const AudioDevice* device = GetDeviceFromId(node_id);
+  if (!device) {
+    VLOG(1) << "RemoveActiveInputNode: Cannot find device id="
+            << "0x" << std::hex << node_id;
+    return;
+  }
+
+  // We do NOT allow to remove the primary active node.
+  if (device->is_input && device->id == active_input_node_id_) {
+    VLOG(1) << "Cannot remove the primary active input node: "
+            << "0x" << std::hex << node_id;
+    return;
+  }
+  if (!device->is_input && device->id == active_output_node_id_) {
+    VLOG(1) << "Cannot remove the primary active output node: "
+            << "0x" << std::hex << node_id;
+    return;
+  }
+  RemoveActiveNodeInternal(node_id);
+}
+
+void CrasAudioHandler::RemoveAllActiveNodes() {
+  for (AudioDeviceMap::const_iterator it = audio_devices_.begin();
+       it != audio_devices_.end();
+       ++it) {
+    RemoveActiveNodeInternal(it->second.id);
   }
 }
 
 bool CrasAudioHandler::has_alternative_input() const {
   return has_alternative_input_;
 }
 
 bool CrasAudioHandler::has_alternative_output() const {
   return has_alternative_output_;
 }
 
 void CrasAudioHandler::SetOutputVolumePercent(int volume_percent) {
-  volume_percent = min(max(volume_percent, 0), 100);
-  if (volume_percent <= kMuteThresholdPercent)
-    volume_percent = 0;
-  output_volume_ = volume_percent;
-
-  if (const AudioDevice* device = GetDeviceFromId(active_output_node_id_))
-    audio_pref_handler_->SetVolumeGainValue(*device, output_volume_);
-
-  SetOutputNodeVolume(active_output_node_id_, output_volume_);
-  FOR_EACH_OBSERVER(AudioObserver, observers_, OnOutputVolumeChanged());
+  // Set all active devices to the same volume.
+  for (AudioDeviceMap::const_iterator it = audio_devices_.begin();
+       it != audio_devices_.end();
+       it++) {
+    const AudioDevice& device = it->second;
+    if (!device.is_input && device.active)
+      SetOutputNodeVolumePercent(device.id, volume_percent);
+  }
 }
 
 // TODO: Rename the 'Percent' to something more meaningful.
 void CrasAudioHandler::SetInputGainPercent(int gain_percent) {
-  // NOTE: We do not sanitize input gain values since the range is completely
-  // dependent on the device.
-  input_gain_ = gain_percent;
-
-  if (const AudioDevice* device = GetDeviceFromId(active_input_node_id_))
-    audio_pref_handler_->SetVolumeGainValue(*device, input_gain_);
-
-  SetInputNodeGain(active_input_node_id_, input_gain_);
-  FOR_EACH_OBSERVER(AudioObserver, observers_, OnInputGainChanged());
+  // TODO(jennyz): Should we set all input devices' gain to the same level?
+  for (AudioDeviceMap::const_iterator it = audio_devices_.begin();
+       it != audio_devices_.end();
+       it++) {
+    const AudioDevice& device = it->second;
+    if (device.is_input && device.active)
+      SetInputNodeGainPercent(active_input_node_id_, gain_percent);
+  }
 }
 
 void CrasAudioHandler::AdjustOutputVolumeByPercent(int adjust_by_percent) {
   SetOutputVolumePercent(output_volume_ + adjust_by_percent);
 }
 
 void CrasAudioHandler::SetOutputMute(bool mute_on) {
   if (!SetOutputMuteInternal(mute_on))
     return;
 
-  if (const AudioDevice* device = GetDeviceFromId(active_output_node_id_)) {
-    DCHECK(!device->is_input);
-    audio_pref_handler_->SetMuteValue(*device, output_mute_on_);
+  // Save the mute state for all active output audio devices.
+  for (AudioDeviceMap::const_iterator it = audio_devices_.begin();
+       it != audio_devices_.end();
+       it++) {
+    const AudioDevice& device = it->second;
+    if (!device.is_input && device.active) {
+      audio_pref_handler_->SetMuteValue(device, output_mute_on_);
+    }
   }
 
   FOR_EACH_OBSERVER(AudioObserver, observers_, OnOutputMuteChanged());
 }
 
 void CrasAudioHandler::AdjustOutputVolumeToAudibleLevel() {
   if (output_volume_ <= kMuteThresholdPercent) {
     // Avoid the situation when sound has been unmuted, but the volume
     // is set to a very low value, so user still can't hear any sound.
     SetOutputVolumePercent(kDefaultUnmuteVolumePercent);
@@ skipping 14 matching lines @@
 }
 
 void CrasAudioHandler::SetActiveInputNode(uint64 node_id) {
   chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->
       SetActiveInputNode(node_id);
   FOR_EACH_OBSERVER(AudioObserver, observers_, OnActiveInputNodeChanged());
 }
 
 void CrasAudioHandler::SetVolumeGainPercentForDevice(uint64 device_id,
                                                      int value) {
-  if (device_id == active_output_node_id_) {
-    SetOutputVolumePercent(value);
+  const AudioDevice* device = GetDeviceFromId(device_id);
+  if (!device)
     return;
-  } else if (device_id == active_input_node_id_) {
-    SetInputGainPercent(value);
-    return;
-  }
 
-  if (const AudioDevice* device = GetDeviceFromId(device_id)) {
-    if (!device->is_input) {
-      value = min(max(value, 0), 100);
-      if (value <= kMuteThresholdPercent)
-        value = 0;
-    }
-    audio_pref_handler_->SetVolumeGainValue(*device, value);
-  }
+  if (device->is_input)
+    SetInputNodeGainPercent(device_id, value);
+  else
+    SetOutputNodeVolumePercent(device_id, value);
 }
 
 void CrasAudioHandler::SetMuteForDevice(uint64 device_id, bool mute_on) {
   if (device_id == active_output_node_id_) {
     SetOutputMute(mute_on);
     return;
   } else if (device_id == active_input_node_id_) {
     VLOG(1) << "SetMuteForDevice sets active input device id="
             << "0x" << std::hex << device_id << " mute=" << mute_on;
     SetInputMute(mute_on);
@@ skipping 58 matching lines @@
 
 void CrasAudioHandler::AudioClientRestarted() {
   // Make sure the logging is enabled in case cras server
   // restarts after crashing.
   LogErrors();
   InitializeAudioState();
 }
 
 void CrasAudioHandler::NodesChanged() {
   // Refresh audio nodes data.
-  GetNodes();
+  GetNodes(true);  // NodesChanged signal received.
 }
 
 void CrasAudioHandler::ActiveOutputNodeChanged(uint64 node_id) {
   if (active_output_node_id_ == node_id)
     return;
 
   // Active audio output device should always be changed by chrome.
   // During system boot, cras may change active input to unknown device 0x1,
   // we don't need to log it, since it is not an valid device.
   if (GetDeviceFromId(node_id)) {
@@ skipping 70 matching lines @@
     return;
   }
   DCHECK(!device->is_input);
   output_mute_on_ = audio_pref_handler_->GetMuteValue(*device);
   output_volume_ = audio_pref_handler_->GetOutputVolumeValue(device);
 
   SetOutputMuteInternal(output_mute_on_);
   SetOutputNodeVolume(active_output_node_id_, output_volume_);
 }
 
+// This sets up the state of an additional active node.
+void CrasAudioHandler::SetupAdditionalActiveAudioNodeState(uint64 node_id) {
+  const AudioDevice* device = GetDeviceFromId(node_id);
+  if (!device) {
+    VLOG(1) << "Can't set up audio state for unknown device id ="
+            << "0x" << std::hex << node_id;
+    return;
+  }
+
+  DCHECK(node_id != active_output_node_id_ && node_id != active_input_node_id_);
+
+  // Note: The mute state is a system wide state, we don't set mute per device,
+  // but just keep the mute state consistent for the active node in prefs.
+  // The output volume should be set to the same value for all active output
+  // devices. For input devices, we don't restore their gain value so far.
+  if (!device->is_input) {
+    audio_pref_handler_->SetMuteValue(*device, IsOutputMuted());
+    SetOutputNodeVolumePercent(node_id, GetOutputVolumePercent());
+  }
+}
+
 void CrasAudioHandler::InitializeAudioState() {
   ApplyAudioPolicy();
-  GetNodes();
+  GetNodes(true);
 }
 
 void CrasAudioHandler::ApplyAudioPolicy() {
   output_mute_locked_ = false;
   if (!audio_pref_handler_->GetAudioOutputAllowedValue()) {
     // Mute the device, but do not update the preference.
     SetOutputMuteInternal(true);
     output_mute_locked_ = true;
   } else {
     // Restore the mute state.
@@ skipping 13 matching lines @@
     SetInputMuteInternal(true);
     input_mute_locked_ = true;
   }
 }
 
 void CrasAudioHandler::SetOutputNodeVolume(uint64 node_id, int volume) {
   chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->
       SetOutputNodeVolume(node_id, volume);
 }
 
+void CrasAudioHandler::SetOutputNodeVolumePercent(uint64 node_id,
+                                                  int volume_percent) {
+  const AudioDevice* device = this->GetDeviceFromId(node_id);
+  if (!device || device->is_input)
+    return;
+
+  volume_percent = min(max(volume_percent, 0), 100);
+  if (volume_percent <= kMuteThresholdPercent)
+    volume_percent = 0;
+  if (node_id == active_output_node_id_)
+    output_volume_ = volume_percent;
+
+  audio_pref_handler_->SetVolumeGainValue(*device, volume_percent);
+
+  if (device->active) {
+    SetOutputNodeVolume(node_id, volume_percent);
+    FOR_EACH_OBSERVER(AudioObserver, observers_, OnOutputVolumeChanged());
+  }
+}
+
 bool  CrasAudioHandler::SetOutputMuteInternal(bool mute_on) {
   if (output_mute_locked_)
     return false;
 
   output_mute_on_ = mute_on;
   chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->
       SetOutputUserMute(mute_on);
   return true;
 }
 
 void CrasAudioHandler::SetInputNodeGain(uint64 node_id, int gain) {
   chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->
       SetInputNodeGain(node_id, gain);
 }
 
+void CrasAudioHandler::SetInputNodeGainPercent(uint64 node_id,
+                                               int gain_percent) {
+  const AudioDevice* device = GetDeviceFromId(node_id);
+  if (!device || !device->is_input)
+    return;
+
+  // NOTE: We do not sanitize input gain values since the range is completely
+  // dependent on the device.
+  if (active_input_node_id_ == node_id)
+    input_gain_ = gain_percent;
+
+  audio_pref_handler_->SetVolumeGainValue(*device, gain_percent);
+
+  if (device->active) {
+    SetInputNodeGain(node_id, gain_percent);
+    FOR_EACH_OBSERVER(AudioObserver, observers_, OnInputGainChanged());
+  }
+}
+
 bool CrasAudioHandler::SetInputMuteInternal(bool mute_on) {
   if (input_mute_locked_)
     return false;
 
-  VLOG(1) << "SetInputMuteInternal sets active input device id="
-          << "0x" << std::hex << active_input_node_id_ << " mute=" << mute_on;
   input_mute_on_ = mute_on;
   chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->
       SetInputMute(mute_on);
   return true;
 }
 
-void CrasAudioHandler::GetNodes() {
-  chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->GetNodes(
-      base::Bind(&CrasAudioHandler::HandleGetNodes,
-                 weak_ptr_factory_.GetWeakPtr()),
-      base::Bind(&CrasAudioHandler::HandleGetNodesError,
-                 weak_ptr_factory_.GetWeakPtr()));
+void CrasAudioHandler::GetNodes(bool nodes_changed) {
+  if (nodes_changed) {
+    chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->GetNodes(
+        base::Bind(&CrasAudioHandler::HandleGetNodes,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&CrasAudioHandler::HandleGetNodesError,
+                   weak_ptr_factory_.GetWeakPtr()));
+  } else {
+    // If GetNodes is not triggered by NodesChanged signal,
+    // HandleGetNodesWithoutNodesChange will just retrieve all the
+    // nodes data from cras without switching active device.
+    // This could be used for diagnostic purpose.
+    chromeos::DBusThreadManager::Get()->GetCrasAudioClient()->GetNodes(
+        base::Bind(&CrasAudioHandler::HandleGetNodesWithoutNodesChange,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&CrasAudioHandler::HandleGetNodesError,
+                   weak_ptr_factory_.GetWeakPtr()));
+  }
 }
 
 bool CrasAudioHandler::ChangeActiveDevice(const AudioDevice& new_active_device,
                                           uint64* current_active_node_id) {
   // If the device we want to switch to is already the current active device,
   // do nothing.
   if (new_active_device.active &&
       new_active_device.id == *current_active_node_id) {
     return false;
   }
@@ skipping 45 matching lines @@
     if (is_input == it->second.is_input)
       ++num_old_devices;
   }
 
   for (AudioNodeList::const_iterator it = new_nodes.begin();
        it != new_nodes.end(); ++it) {
     if (is_input == it->is_input) {
       ++num_new_devices;
       // Look to see if the new device not in the old device list.
       AudioDevice device(*it);
-      if (FoundNewDevice(device))
+      if (FoundNewOrChangedDevice(device))
         return true;
     }
   }
   return num_old_devices != num_new_devices;
 }
 
-bool CrasAudioHandler::FoundNewDevice(const AudioDevice& device) {
+bool CrasAudioHandler::FoundNewOrChangedDevice(const AudioDevice& device) {
   const AudioDevice* device_found = GetDeviceFromId(device.id);
   if (!device_found)
     return true;
 
   if (!IsSameAudioDevice(device, *device_found)) {
     LOG(WARNING) << "Different Audio devices with same id:"
         << " new device: " << device.ToString()
         << " old device: " << device_found->ToString();
     return true;
+  } else if (device.active != device_found->active) {
+    return true;
+  }
+
+  return false;
+}
+
+bool CrasAudioHandler::HasAdditionalActiveOutputNode() const {

[rkc, 2014/09/24 19:45:30]

No longer used.

[jennyz, 2014/09/24 20:47:18]

Done.

+  for (AudioDeviceMap::const_iterator it = audio_devices_.begin();
+       it != audio_devices_.end();
+       ++it) {
+    if (active_output_node_id_ && !it->second.is_input && it->second.active &&
+        it->second.id != active_output_node_id_) {
+      return true;
+    }
   }
   return false;
 }
 
-// Sanitize the audio node data. When a device is plugged in or unplugged, there
-// should be only one NodesChanged signal from cras. However, we've observed
-// the case that multiple NodesChanged signals being sent from cras. After the
-// first NodesChanged being processed, chrome sets the active node properly.
-// However, the NodesChanged received after the first one, can return stale
-// nodes data in GetNodes call, the staled nodes data does not reflect the
-// latest active node state. Since active audio node should only be set by
-// chrome, the inconsistent data from cras could be the result of stale data
-// described above and sanitized.
-AudioDevice CrasAudioHandler::GetSanitizedAudioDevice(const AudioNode& node) {
-  AudioDevice device(node);
-  if (device.is_input) {
-    if (device.active && device.id != active_input_node_id_) {
-      LOG(WARNING) << "Stale audio device data, should not be active: "
-          << " device = " << device.ToString()
-          << " current active input node id = 0x" << std::hex
-          << active_input_node_id_;
-      device.active = false;
-    } else if (device.id == active_input_node_id_ && !device.active) {
-      LOG(WARNING) << "Stale audio device data, should be active:"
-          << " device = " << device.ToString()
-          << " current active input node id = 0x" << std::hex
-          << active_input_node_id_;
-      device.active = true;
-    }
-  } else {
-    if (device.active && device.id != active_output_node_id_) {
-      LOG(WARNING) << "Stale audio device data, should not be active: "
-          << " device = " << device.ToString()
-          << " current active output node id = 0x" << std::hex
-          << active_output_node_id_;
-      device.active = false;
-    } else if (device.id == active_output_node_id_ && !device.active) {
-      LOG(WARNING) << "Stale audio device data, should be active:"
-          << " device = " << device.ToString()
-          << " current active output node id = 0x" << std::hex
-          << active_output_node_id_;
-      device.active = true;
+bool CrasAudioHandler::HasAdditionalActiveInputNode() const {

[rkc, 2014/09/24 19:45:30]

Ditto.

[jennyz, 2014/09/24 20:47:18]

Done.

+  for (AudioDeviceMap::const_iterator it = audio_devices_.begin();
+       it != audio_devices_.end();
+       ++it) {
+    if (active_input_node_id_ && it->second.is_input && it->second.active &&
+        it->second.id != active_input_node_id_) {
+      return true;
     }
   }
-  return device;
+  return false;
 }
 
 void CrasAudioHandler::UpdateDevicesAndSwitchActive(
     const AudioNodeList& nodes) {
   size_t old_audio_devices_size = audio_devices_.size();
   bool output_devices_changed = HasDeviceChange(nodes, false);
   bool input_devices_changed = HasDeviceChange(nodes, true);
   audio_devices_.clear();
   has_alternative_input_ = false;
   has_alternative_output_ = false;
 
   while (!input_devices_pq_.empty())
     input_devices_pq_.pop();
   while (!output_devices_pq_.empty())
     output_devices_pq_.pop();
 
   for (size_t i = 0; i < nodes.size(); ++i) {
-    AudioDevice device = GetSanitizedAudioDevice(nodes[i]);
+    AudioDevice device(nodes[i]);
     audio_devices_[device.id] = device;
 
     if (!has_alternative_input_ &&
         device.is_input &&
         device.type != AUDIO_TYPE_INTERNAL_MIC &&
         device.type != AUDIO_TYPE_KEYBOARD_MIC) {
       has_alternative_input_ = true;
     } else if (!has_alternative_output_ &&
                !device.is_input &&
                device.type != AUDIO_TYPE_INTERNAL_SPEAKER) {
@@ skipping 28 matching lines @@
                                       bool success) {
   if (!success) {
     LOG_IF(ERROR, log_errors_) << "Failed to retrieve audio nodes data";
     return;
   }
 
   UpdateDevicesAndSwitchActive(node_list);
   FOR_EACH_OBSERVER(AudioObserver, observers_, OnAudioNodesChanged());
 }
 
+void CrasAudioHandler::HandleGetNodesWithoutNodesChange(
+    const chromeos::AudioNodeList& node_list,
+    bool success) {
+  if (!success) {
+    LOG_IF(ERROR, log_errors_) << "Failed to retrieve audio nodes data";
+    return;
+  }
+
+  // Just refresh the audio_devices_ with the latest audio_list from cras.
+  for (size_t i = 0; i < node_list.size(); ++i) {
+    AudioDevice device(node_list[i]);
+    audio_devices_[device.id] = device;
+  }
+}
+
 void CrasAudioHandler::HandleGetNodesError(const std::string& error_name,
                                            const std::string& error_msg) {
   LOG_IF(ERROR, log_errors_) << "Failed to call GetNodes: "
       << error_name  << ": " << error_msg;
 }
+
+void CrasAudioHandler::AddAdditionalActiveNode(uint64 node_id) {
+  const AudioDevice* device = GetDeviceFromId(node_id);
+  if (!device) {
+    VLOG(1) << "AddActiveInputNode: Cannot find device id="
+            << "0x" << std::hex << node_id;
+    return;
+  }
+
+  audio_devices_[node_id].active = true;
+  SetupAdditionalActiveAudioNodeState(node_id);
+
+  if (device->is_input) {
+    DCHECK(node_id != active_input_node_id_);
+    chromeos::DBusThreadManager::Get()
+        ->GetCrasAudioClient()
+        ->AddActiveInputNode(node_id);
+    FOR_EACH_OBSERVER(AudioObserver, observers_, OnActiveInputNodeChanged());
+  } else {
+    DCHECK(node_id != active_output_node_id_);
+    chromeos::DBusThreadManager::Get()
+        ->GetCrasAudioClient()
+        ->AddActiveOutputNode(node_id);
+    FOR_EACH_OBSERVER(AudioObserver, observers_, OnActiveOutputNodeChanged());
+  }
+}
+
+void CrasAudioHandler::RemoveActiveNodeInternal(uint64 node_id) {
+  const AudioDevice* device = GetDeviceFromId(node_id);
+  if (!device) {
+    VLOG(1) << "RemoveActiveInputNode: Cannot find device id="
+            << "0x" << std::hex << node_id;
+    return;
+  }
+
+  audio_devices_[node_id].active = false;
+  if (device->is_input) {
+    if (node_id == active_input_node_id_)
+      active_input_node_id_ = 0;
+    chromeos::DBusThreadManager::Get()
+        ->GetCrasAudioClient()
+        ->RemoveActiveInputNode(node_id);
+    FOR_EACH_OBSERVER(AudioObserver, observers_, OnActiveInputNodeChanged());
+  } else {
+    if (node_id == active_output_node_id_)
+      active_output_node_id_ = 0;
+    chromeos::DBusThreadManager::Get()
+        ->GetCrasAudioClient()
+        ->RemoveActiveOutputNode(node_id);
+  }
+  FOR_EACH_OBSERVER(AudioObserver, observers_, OnActiveOutputNodeChanged());
+}
+
 }  // namespace chromeos