Use ScopedTaskEnvironment instead of MessageLoopForIO in net unit tests.
ScopedTaskEnvironment allows usage of ThreadTaskRunnerHandle and
base/task_scheduler/post_task.h within its scope. It should be
instantiated in everytest that uses either of these APIs
(i.e. no test should instantiate a MessageLoop directly).
Switching from MessageLoopForIO to ScopedTaskEnvironment in
NetTestSuite allows Scoped(Async)TaskScheduler to be removed
from individual net unittests.
Motivation for ScopedTaskEnvironment can be found in:
https://docs.google.com/document/d/1QabRo8c7D9LsYY3cEcaPQbOCLo8Tu-6VLykYXyl3Pkk/edit
BUG=708584
Review-Url: https://codereview.chromium.org/2839663002
Cr-Commit-Position: refs/heads/master@{#471073}
17 files changed
