[WIP] - trying out some state machine ideas.

media/base/state.cc

+// Copyright 2016 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 "media/base/state.h"
+
+namespace media {
+
+State::State() {}
+
+State::~State() {}
+
+void State::RegisterClient(Client* client) {
+  clients_.insert(client);
+}
+
+void State::UnregisterClient(Client* client) {
+  clients_.erase(client);
+}
+
+void State::StateChanged() {
+  for (Client* client : clients_)
+    client->OnStateChanged();
+}
+
+}  // namespace media