GitLab

The Ready callback passed to SetReadyCallback is executed
on the task runner thread, and not the UI thread.

This causes a crash in startup when launching Chrome.

Also adding a DCHECK to catch this in tests in the
future.

Bug: 820925, 734095
Change-Id: I59d2b152bbc6538d857f3e6884544217b347885e
Reviewed-on: https://chromium-review.googlesource.com/959017
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542532}