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..955c05192d7d7a36fa5c78dcb2b8999f20336604 100644
--- a/chrome/browser/ui/webui/media_router/media_router_ui.h
+++ b/chrome/browser/ui/webui/media_router/media_router_ui.h
@@ -163,10 +163,8 @@ class MediaRouterUI : public ConstrainedWebDialogUI,
  private:
   FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest, SortedSinks);
   FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest, SortSinksByIconType);
-  FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest,
-                           UIMediaRoutesObserverFiltersNonDisplayRoutes);
-  FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest,
-      UIMediaRoutesObserverFiltersNonDisplayJoinableRoutes);
+  FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest, FilterNonDisplayRoutes);
+  FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest, FilterNonDisplayJoinableRoutes);
   FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest,
       UIMediaRoutesObserverAssignsCurrentCastModes);
   FRIEND_TEST_ALL_PREFIXES(MediaRouterUITest,
@@ -270,6 +268,10 @@ class MediaRouterUI : public ConstrainedWebDialogUI,
   // |handler_|.
   void UpdateCastModes();
 
+  // Updates the routes-to-cast-modes mapping in |current_cast_modes_| to match
+  // the value of |routes_|.
+  void UpdateCurrentCastModes();
+
   // Returns the default presentation request's frame URL if there is one.
   // Otherwise returns an empty GURL.
   GURL GetFrameURL() const;