[Media Controls] Prevent showing dummy media notifications.

This change prevents a blank media notification from being shown (due
to a partially implemented feature) unless the appropriate feature
flags are enabled.


Bug: 1134356, b/169946872
Change-Id: I54a0575a302e4215f9d3fd98cd39af4d38f944ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2453893Reviewed-by: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Commit-Queue: John Williams <jrw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814358}

chrome/browser/ui/global_media_controls/media_notification_service.cc

@@ -325,8 +325,6 @@ MediaNotificationService::MediaNotificationService(Profile* profile,
             base::BindRepeating(
                 &MediaNotificationService::OnCastNotificationsChanged,
                 base::Unretained(this)));
-    presentation_request_notification_provider_ =
-        std::make_unique<PresentationRequestNotificationProvider>(this);
   }
   if (media_router::GlobalMediaControlsCastStartStopEnabled()) {
     presentation_request_notification_provider_ =