[Downloads] Don't use ScopedProfileKeepAlive for OTR profiles

ScopedProfileKeepAlive is not meant for use with OTR profiles, so this
caused a failed DCHECK() when a downloading a file in Incognito (with
DestroyProfileOnBrowserClose=true).

Bug: 88586
Change-Id: I1aff2cadf62ab1bd56a0b44e9154d6843f92cc89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2622873Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842616}

chrome/browser/download/download_status_updater.cc

@@ -146,9 +146,12 @@ void DownloadStatusUpdater::UpdateProfileKeepAlive(
     return;
   }
 
-  // Are we already holding a keepalive?
   Profile* profile = Profile::FromBrowserContext(manager->GetBrowserContext());
   DCHECK(profile);
+  if (profile->IsOffTheRecord())
+    return;
+
+  // Are we already holding a keepalive?
   bool already_has_keep_alive =
       (profile_keep_alives_.find(profile) != profile_keep_alives_.end());