Change DataReductionProxy to use NetworkChangeObserver

NetworkChangeNotifier::IPAddress Observer is being deprecated.
This CL migrates DataReductionProxy to use NetworkChangeObserver instead.

Bug: 754695
Change-Id: I473ad45e88cff01a9f33a183033a9d86f59aef4e
Reviewed-on: https://chromium-review.googlesource.com/1133330
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Lily Houghton <lilyhoughton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575549}
6 files changed