Use ScopedTaskEnvironment instead of MessageLoop in /chrome/browser/web_applications

MessageLoop will go away, eventually.

ScopedTaskEnvironment will per default start a ThreadPool, which should
be fine in most of the cases. If you belive your test needs to make sure
that no ThreadPool runs let me know and I will update the patch.

BUG=891670
This CL was uploaded by git cl split.

R=alancutter@chromium.org

Change-Id: Ic08e8e019e32886e935b91fbe3996c05ecec970d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1648202
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669554}
1 file changed