Let NetworkService manage the NetworkChangeNotifier in unit tests

We jumped through a lot of hoops to deal with the NetworkChangeNotifier
leaking due to the NetworkService leaking, but now that
NetworkService is deleted between tests, we can remove the special
NetworkChangeNotifier test logic.

Bug: 901092
Change-Id: I49bd022fe2679f1b2ef7b716177af1f11df1457e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1658644
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Robbie McElrath <rmcelrath@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669776}
8 files changed