Remove references of MessageLoopForIO in /jingle

MessageLoopForIO will go away soon use ScopedTaskEnvironment instead.

ScopedTaskEnvironment will per default start a ThreadPool, which should
be fine in most of the cases. If you believe 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=zea@chromium.org

Change-Id: I85626fd1fddb7d36b61b60574b5a6868630d4ed5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733550
Reviewed-by: Nicolas Zea <zea@chromium.org>
Commit-Queue: Carlos Caballero <carlscab@google.com>
Cr-Commit-Position: refs/heads/master@{#685560}
2 files changed