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

chrome/browser/media/router/media_router_base.h

Index: chrome/browser/media/router/media_router_base.h
diff --git a/chrome/browser/media/router/media_router_base.h b/chrome/browser/media/router/media_router_base.h
index 45c0f261c24156c24a2fd1b0b1e1d1e23d5d76f6..c1b46e91b01f732482a2898575419741408858aa 100644
--- a/chrome/browser/media/router/media_router_base.h
+++ b/chrome/browser/media/router/media_router_base.h
@@ -32,6 +32,8 @@ class MediaRouterBase : public MediaRouter {
   // This will terminate all incognito media routes.
   void OnIncognitoProfileShutdown() override;
 
+  std::vector<MediaRoute> GetCurrentRoutes() const override;
+
  protected:
   FRIEND_TEST_ALL_PREFIXES(MediaRouterMojoImplTest,
                            PresentationConnectionStateChangedCallback);
@@ -66,6 +68,7 @@ class MediaRouterBase : public MediaRouter {
       presentation_connection_state_callbacks_;
 
  private:
+  friend class MediaRouterBaseTest;
   friend class MediaRouterFactory;
   friend class MediaRouterMojoTest;