Migrate CreateFileSystemContext() to TaskScheduler.

This is take #2 after https://codereview.chromium.org/2883403002

R=tzik@chromium.org

Bug: 667892
Change-Id: Ibb08b11efecdb380fb7adff143ee2ba48b726380
Reviewed-on: https://chromium-review.googlesource.com/585588
Reviewed-by: Taiju Tsuiki <tzik@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#489602}
1 file changed