Network services: add tools/perf/contrib/network_service.

The folder will be used to host benchmarks for measuring perf of Chrome with
the network service enabled.

Eventually we won't need this folder when the network service is enabled by
default and the old network-in-browser-process code path is removed.

BUG=717738,598073
R=nednguyen@google.com

Review-Url: https://codereview.chromium.org/2877553003 .
Cr-Commit-Position: refs/heads/master@{#471048}

tools/perf/contrib/network_service/OWNERS

+file://content/network/OWNERS