GitLab

This clears all prefetches and timers in the search prefetch service
when the user clears their data (time is not considered in determining
which prefetches to clear).

Added a couple of nullptr checks to prefetch service as well.

Bug: 1138645, 1138644
Change-Id: Icbfbd0c7363e55f758c801faa91b100eaa7a365f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2493727Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Robert Ogden <robertogden@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822667}