[Media Router] Notify MRUI of a media status update when it starts observing

chrome/browser/media/router/mojo/media_route_controller.cc

Index: chrome/browser/media/router/mojo/media_route_controller.cc
diff --git a/chrome/browser/media/router/mojo/media_route_controller.cc b/chrome/browser/media/router/mojo/media_route_controller.cc
index 425dcd4ab99568b99f52078d4c02274af23194af..72f25cb91dc80b90e266d2fc28b4c65047473c9e 100644
--- a/chrome/browser/media/router/mojo/media_route_controller.cc
+++ b/chrome/browser/media/router/mojo/media_route_controller.cc
@@ -21,6 +21,11 @@ MediaRouteController::Observer::~Observer() {
     controller_->RemoveObserver(this);
 }
 
+void MediaRouteController::Observer::CheckForMediaStatusUpdates() {
+  if (controller_ && controller_->current_media_status().has_value())
+    OnMediaStatusUpdated(controller_->current_media_status().value());
+}
+
 void MediaRouteController::Observer::InvalidateController() {
   controller_ = nullptr;
   OnControllerInvalidated();
@@ -69,6 +74,7 @@ void MediaRouteController::SetVolume(float volume) const {
 
 void MediaRouteController::OnMediaStatusUpdated(const MediaStatus& status) {
   DCHECK(is_valid_);
+  current_media_status_ = base::make_optional<MediaStatus>(MediaStatus(status));
   for (Observer& observer : observers_)
     observer.OnMediaStatusUpdated(status);
 }