[Media Router] Add Media Router Mojo impl code.

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 "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.
+  // Invoked when the list of routes and their associated sinks have been
+  // updated.
+  // Implementations may not perform operations that modify the Media Router's
+  // observer list. In particular, invoking this observer's destructor within
+  // OnRoutesUpdated will result in undefined behavior.
   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_