Make NetworkConnectionTracker survive network service crashes and restarts

This CL is to mirror tbansal@'s CL
(https://chromium-review.googlesource.com/1058528) to make
NetworkConnectionTracker survice network service's crashes and restarts.

Bug: 821009
Change-Id: Iec33797c0fd0ce12a8e5fdab9fda0a710eb9a528
Reviewed-on: https://chromium-review.googlesource.com/1120738
Commit-Queue: Helen Li <xunjieli@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574314}
6 files changed