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

chrome/browser/ui/webui/media_router/media_router_ui.h

Index: chrome/browser/ui/webui/media_router/media_router_ui.h
diff --git a/chrome/browser/ui/webui/media_router/media_router_ui.h b/chrome/browser/ui/webui/media_router/media_router_ui.h
index a17ae34dc1b68ec87f9a951184ecb1a329690ad5..6b9f979a3444dc94072b44c1c7baba6f55edeb21 100644
--- a/chrome/browser/ui/webui/media_router/media_router_ui.h
+++ b/chrome/browser/ui/webui/media_router/media_router_ui.h
@@ -147,6 +147,8 @@ class MediaRouterUI : public ConstrainedWebDialogUI,
   // Marked virtual for tests.
   virtual const std::string& GetRouteProviderExtensionId() const;
 
+  const std::vector<MediaRoute>& GetRoutes();
+
   // Called to track UI metrics.
   void SetUIInitializationTimer(const base::Time& start_time);
   void OnUIInitiallyLoaded();
@@ -286,6 +288,8 @@ class MediaRouterUI : public ConstrainedWebDialogUI,
   // Set to true by |handler_| when the UI has been initialized.
   bool ui_initialized_;
 
+  bool initial_routes_received_;
+
   // Set to -1 if not tracking a pending route request.
   int current_route_request_id_;