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;
+
+  // MSVC prior to 2013 doesn't have a round function.  The below code is not
+  // conformant to C99 round(), but since we know that 0 <= level <= 100, it
+  // should be ok.
+  return static_cast<int>(level + 0.5);
+}
+
+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>
+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