Remove references of MessageLoopForIO in /chrome/browser/data_reduction_proxy/data_reduction_proxy_settings_unittest_android.cc

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=dtrainor@chromium.org

Change-Id: Ie7b352f51f26993d3408a37ba1a88803d43f8151
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733593
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683702}