thermald: get rid of base::MessgaeLoop.

base::MessgaeLoop is deprecated.

Use base::SingleThreadTaskExecutor for production code, and
base::test::SingleThreadTaskEnvironment for unittest.

BUG=chromium:1094927
TEST=unittest thermald

Change-Id: Ib0254dfd466449cdf475d94964da2f881b62bded
Reviewed-on: https://chrome-internal-review.googlesource.com/c/chromeos/thermald/+/3367074
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Qijiang Fan <fqj@google.com>
Tested-by: Qijiang Fan <fqj@google.com>
3 files changed