[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_routes_observer.h

+// 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 CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTES_OBSERVER_H_
+#define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTES_OBSERVER_H_
+
+#include <vector>
+
+#include "chrome/browser/media/router/media_route.h"
+#include "chrome/browser/media/router/media_sink.h"
+
+namespace media_router {
+
+struct RoutesQueryResult {
+  RoutesQueryResult();
+  ~RoutesQueryResult();
+
+  std::vector<MediaRoute> routes;
+  std::vector<MediaSink> sinks;
+};
+
+// Base class for observing when the set of MediaRoutes and their associated
+// MediaSinks have been updated.
+class MediaRoutesObserver {
+ public:
+  MediaRoutesObserver();
+  virtual ~MediaRoutesObserver();
+
+  // This function is invoked when the list of routes and their associated
+  // sinks have been updated.
+  virtual void OnRoutesUpdated(const RoutesQueryResult& result) {}
+
+ private:
+  friend class MediaRouterImpl;
+
+  // This field will be set by MediaRouterImpl, and must be false by

[Kevin Marshall, 2015/04/01 17:00:19]

Can you describe the purpose of this field too?

Also, since this is a private member of a base class that never modifies it -
how will this field ever be set to true? 

[imcheng, 2015/04/01 18:10:09]

Add documentation. The bit will be set by MediaRouterImpl which is a friend of
this class.

+  // this instance's destruction.
+  bool registered_;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTES_OBSERVER_H_