Update AnnouncementNotificationService for ephemeral Guest profiles.

Announcement notification service is disabled for Guest profiles. This
CL updates it to be also disabled for ephemeral Guest profiles.

This change is behind disabled |EnableEphemeralGuestProfilesOnDesktop|
flag.
Please see go/ephemeral-guest-profiles for more context.

Bug: 1125474
Change-Id: I07188559a37470dc3f4dae3ee595a6cbae4cf2b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2470519Reviewed-by: Xing Liu <xingliu@chromium.org>
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817361}

chrome/browser/updates/announcement_notification/announcement_notification_service.cc

@@ -266,7 +266,8 @@ bool AnnouncementNotificationService::CanOpenAnnouncement(Profile* profile) {
   if (!profile)
     return false;
 
-  return !(profile->IsGuestSession() || profile->IsSystemProfile());
+  return !(profile->IsGuestSession() || profile->IsEphemeralGuestProfile() ||
+           profile->IsSystemProfile());
 }
 
 AnnouncementNotificationService::AnnouncementNotificationService() = default;