Make //ios validation_rules_storage_factory match //chrome's

JsonPrefStore grabs an independent SequencedTaskRunner per store by
default now.

R=mahmadi@chromium.org

Bug: 667892
Change-Id: Ied4fb6b10bb4c6cc8be4fc66fedd8a9c0ff64a74
Reviewed-on: https://chromium-review.googlesource.com/600508
Reviewed-by: Rohit Rao (ping after 24h) <rohitrao@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492039}
1 file changed