Add GetCurrentRoutes() to MediaRouter API, ensure dialog has routes at init

chrome/browser/media/router/media_router.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_ROUTER_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 163 matching lines @@
   // caller destroys the Subscription object.
   virtual std::unique_ptr<PresentationConnectionStateSubscription>
   AddPresentationConnectionStateChangedCallback(
       const MediaRoute::Id& route_id,
       const content::PresentationConnectionStateChangedCallback& callback) = 0;
 
   // Called when the incognito profile for this instance is being shut down.
   // This will terminate all incognito media routes.
   virtual void OnIncognitoProfileShutdown() = 0;
 
+  // Returns the media routes that currently exist. To get notified whenever
+  // there is a change to the media routes, subclass MediaRoutesObserver.
+  virtual std::vector<MediaRoute> GetCurrentRoutes() const = 0;
+
  private:
   friend class IssuesObserver;
   friend class MediaSinksObserver;
   friend class MediaRoutesObserver;
   friend class PresentationConnectionStateObserver;
   friend class RouteMessageObserver;
 
   // The following functions are called by friend Observer classes above.
 
   // Registers |observer| with this MediaRouter. |observer| specifies a media
@@ skipping 43 matching lines @@
 
   // Unregisters a previously registered RouteMessagesObserver. |observer| will
   // stop receiving further updates.
   virtual void UnregisterRouteMessageObserver(
       RouteMessageObserver* observer) = 0;
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_H_