libchromeos: Use chromeos::MessageLoop in Streams classes.

This patch replaces the calls to base::MessageLoopForIO with calls to
chromeos::MessageLoop in the Stream classes. This allows to use Streams
with other message loops.

BUG=chromium:499886
TEST=Unittests updated.

Reviewed-on: https://chromium-review.googlesource.com/290541
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Trybot-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>

(cherry-picked from
 https://chromium.googlesource.com/chromiumos/platform2 at 8f3af00c53aef99d1f7fab2f1d8035a9b5b4f7e9)

Change-Id: I04c78b0dc258a2eff9ab0b4eb8559f4f02feab46
10 files changed