[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();

[Kevin M, 2015/03/26 20:50:14]

Is this needed? Default ctor and dtor should suffice?

[imcheng, 2015/03/26 23:33:13]

Unfortunately it will not compile without explicitly defining the ctor/dtor due
to this error: [chromium-style] Complex class/struct needs an explicit
out-of-line destructor.

+  ~RoutesQueryResult();
+
+  std::vector<MediaRoute> routes;
+  std::vector<MediaSink> sinks;
+};
+
+// Interface for observing when the set of MediaRoutes and their associated
+// MediaSinks have been updated.
+class MediaRoutesObserver {
+ public:
+  virtual ~MediaRoutesObserver() {}
+
+  // This function is invoked when the list of routes and their associated
+  // sinks have been updated.
+  virtual void OnRoutesUpdated(const RoutesQueryResult& result) = 0;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTES_OBSERVER_H_