GitLab

Currently, the "Sync is possible but disabled by the user" state is very
hard to reach: On non-Android, the only way is to trigger a "Reset Sync"
from the dashboard (and on non-ChromeOS, that also signs you out, so
there's really no way at all to reach that state).
This CL adds buttons to request start/stop to about:sync-internals, to
make it easy to reach this state for testing.

Bug: 839834
Change-Id: Ie0757f3c9a7658ac281adbcdf227fc4e6807e6ac
Reviewed-on: https://chromium-review.googlesource.com/1113445Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570025}