Prevent use-after-free in SiteEngagementService.

The profile and its KeyedServices are normally destroyed before the
TaskScheduler shuts down background threads, so the background task to
record site engagement metrics needs to avoid using any members of
SiteEngagementService

Bug: 900022
Change-Id: Ibdebbd5a64d59fad29b7715be3557eeed411d741
Reviewed-on: https://chromium-review.googlesource.com/c/1326441
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606781}
1 file changed