Remove GetBlockingPool call from shell_prefs.cc

These files are only accessed through the JsonPrefStore created here,
so we don't need to worry about getting a unique SequencedWorkerPool.

Bug: 689520
Change-Id: I4c609c8b76ff07bf6c43c6d67efa3edf65c374f4
Reviewed-on: https://chromium-review.googlesource.com/582587
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490088}
1 file changed