[Chromecast] Add new volume control API to CastMediaShlib

chromecast/media/base/audio_device_ids.h

+// Copyright 2017 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.
+
+#ifndef CHROMECAST_MEDIA_BASE_AUDIO_DEVICE_IDS_H_
+#define CHROMECAST_MEDIA_BASE_AUDIO_DEVICE_IDS_H_
+
+namespace chromecast {
+namespace media {
+
+extern const char kAlarmAudioDeviceId[];
+extern const char kTtsAudioDeviceId[];
+
+// Local-only audio (don't send over multiroom).
+extern const char kLocalAudioDeviceId[];
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_MEDIA_BASE_AUDIO_DEVICE_IDS_H_