Migration of font thread to sequence tasks runner

This CL is removing the thread and using a task runner instead.

I propose to continue this migration by renaming the thread
service since it's no longer a thread.

R=fdoray@chromium.org, gab@chromium.org
BUG=936569

Change-Id: If65dfd41406d13c9f69036d71e75242ef29f9b1d
Reviewed-on: https://chromium-review.googlesource.com/c/1492369
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636527}
4 files changed