Add an initial revision of an audio server.

services/media/audio/fwd_decls.h

Index: services/media/audio/fwd_decls.h
diff --git a/services/media/audio/fwd_decls.h b/services/media/audio/fwd_decls.h
new file mode 100644
index 0000000000000000000000000000000000000000..c4f2c9e4fee478c0ef7d64046b17c6fbf1eefa21
--- /dev/null
+++ b/services/media/audio/fwd_decls.h
@@ -0,0 +1,44 @@
+// Copyright 2015 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 SERVICES_MEDIA_AUDIO_FWD_DECLS_H__
+#define SERVICES_MEDIA_AUDIO_FWD_DECLS_H__
+
+#include <memory>
+#include <set>
+
+namespace mojo {
+namespace media {
+namespace audio {
+
+class AudioOutput;
+class AudioOutputManager;
+class AudioServerImpl;
+class AudioTrackImpl;
+class AudioTrackToOutputLink;
+
+using AudioOutputPtr = std::shared_ptr<AudioOutput>;
+using AudioOutputSet = std::set<AudioOutputPtr,
+                                std::owner_less<AudioOutputPtr>>;
+using AudioOutputWeakPtr = std::weak_ptr<AudioOutput>;
+using AudioOutputWeakSet = std::set<AudioOutputWeakPtr,
+                                    std::owner_less<AudioOutputWeakPtr>>;
+
+using AudioTrackImplPtr = std::shared_ptr<AudioTrackImpl>;
+using AudioTrackImplSet = std::set<AudioTrackImplPtr,
+                                  std::owner_less<AudioTrackImplPtr>>;
+using AudioTrackImplWeakPtr = std::weak_ptr<AudioTrackImpl>;
+using AudioTrackImplWeakSet = std::set<AudioTrackImplWeakPtr,
+                                      std::owner_less<AudioTrackImplWeakPtr>>;
+
+using AudioTrackToOutputLinkPtr = std::shared_ptr<AudioTrackToOutputLink>;
+using AudioTrackToOutputLinkSet =
+  std::set<AudioTrackToOutputLinkPtr,
+           std::owner_less<AudioTrackToOutputLinkPtr>>;
+
+}  // namespace audio
+}  // namespace media
+}  // namespace mojo
+
+#endif  // SERVICES_MEDIA_AUDIO_FWD_DECLS_H__