Enable the volume slider in Ash for windows.

ash/system/win/audio/tray_audio_delegate_win.cc

+// Copyright 2014 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 "ash/system/win/audio/tray_audio_delegate_win.h"
+
+#include <audiopolicy.h>
+#include <cmath>
+
+#include "grit/ash_resources.h"
+#include "grit/ash_strings.h"
+#include "media/audio/win/core_audio_util_win.h"
+
+using base::win::ScopedComPtr;
+
+namespace {
+
+// Volume value which should be considered as muted in range [0, 100].
+const int kMuteThresholdPercent = 1;
+
+// Lowest volume which is considered to be audible in the range [0, 100].
+const int kDefaultUnmuteVolumePercent = 4;
+
+}  // namespace
+
+namespace ash  {
+namespace system {
+
+void TrayAudioDelegateWin::AdjustOutputVolumeToAudibleLevel() {
+  if (GetOutputVolumeLevel() <= kMuteThresholdPercent)
+    SetOutputVolumeLevel(kDefaultUnmuteVolumePercent);
+}
+
+int TrayAudioDelegateWin::GetOutputDefaultVolumeMuteLevel() {
+  return kMuteThresholdPercent;
+}
+
+int TrayAudioDelegateWin::GetOutputVolumeLevel() {
+  ScopedComPtr<ISimpleAudioVolume> volume_control =
+      CreateDefaultVolumeControl();
+
+  float level = 0.0f;
+  if (FAILED(volume_control->GetMasterVolume(&level)))
+    return 0;
+
+  return static_cast<int>(std::roundf(level * 100.0f));
+}
+
+int TrayAudioDelegateWin::GetActiveOutputDeviceIconId() {
+  return kNoAudioDeviceIcon;
+}
+
+bool TrayAudioDelegateWin::HasAlternativeSources() {
+  return false;
+}
+
+bool TrayAudioDelegateWin::IsOutputAudioMuted() {
+  ScopedComPtr<ISimpleAudioVolume> volume_control =
+      CreateDefaultVolumeControl();
+
+  BOOL mute = FALSE;
+  if (FAILED(volume_control->GetMute(&mute)))
+    return false;
+
+  return !!mute;
+}
+
+void TrayAudioDelegateWin::SetOutputAudioIsMuted(bool is_muted) {
+  ScopedComPtr<ISimpleAudioVolume> volume_control =
+      CreateDefaultVolumeControl();
+
+  volume_control->SetMute(is_muted, NULL);
+}
+
+void TrayAudioDelegateWin::SetOutputVolumeLevel(int level) {
+  ScopedComPtr<ISimpleAudioVolume> volume_control =
+      CreateDefaultVolumeControl();
+
+  float volume_level = static_cast<float>(level) / 100.0f;
+  volume_control->SetMasterVolume(volume_level, NULL);
+}
+
+ScopedComPtr<ISimpleAudioVolume>

[henrika (OOO until Aug 14), 2014/02/26 09:10:05]

It is not clear to me why you call this method in every method which needs the
volume control. Would it not be possible to create a volume control once (during
construction) and use that after. Perhaps I am missing something regarding the
use case.
Perhaps tommi@ knows the answer as well.

[tommi (sloooow) - chröme, 2014/02/26 11:10:44]

If these methods are infrequently called, then I think it's fine as is.  Caching
the default device could be problematic if it changes and right now the code
avoids problems because of that.

[zturner, 2014/02/26 17:50:29]

Yes, the default device changing is exactly the reason I did it this way.

+TrayAudioDelegateWin::CreateDefaultVolumeControl() {
+  ScopedComPtr<ISimpleAudioVolume> volume_control;
+  ScopedComPtr<IAudioSessionManager> session_manager;
+
+  ScopedComPtr<IMMDevice> device =
+      media::CoreAudioUtil::CreateDefaultDevice(eRender, eConsole);
+  if (FAILED(device->Activate(__uuidof(IAudioSessionManager), CLSCTX_ALL, NULL,
+             session_manager.ReceiveVoid()))) {
+    return volume_control;
+  }
+
+  session_manager->GetSimpleAudioVolume(NULL, FALSE,
+      volume_control.Receive());
+
+  return volume_control;
+}
+
+}  // namespace system
+}  // namespace ash