[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_routes_observer.h

Index: chrome/browser/media/router/media_routes_observer.h
diff --git a/chrome/browser/media/router/media_routes_observer.h b/chrome/browser/media/router/media_routes_observer.h
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+// 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 "base/macros.h"
+#include "chrome/browser/media/router/media_route.h"
+
+namespace media_router {
+
+class MediaRouter;
+
+// Base class for observing when the set of MediaRoutes and their associated
+// MediaSinks have been updated.
+class MediaRoutesObserver {
+ public:
+  explicit MediaRoutesObserver(MediaRouter* router);
+  virtual ~MediaRoutesObserver();
+
+  // This function is invoked when the list of routes and their associated
+  // sinks have been updated. Routes included in the list are created either
+  // locally or remotely.
+  virtual void OnRoutesUpdated(const std::vector<MediaRoute>& routes) {}
+
+ private:
+  MediaRouter* router_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaRoutesObserver);
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTES_OBSERVER_H_