Support of specify local prebuilt network service file.
Support of specify local prebuilt network service file.

This change is chromium part of
https://codereview.chromium.org/921053003/

And out-of-date TODO is removed as well.

TEST=
BUG=458409

Review URL: https://codereview.chromium.org/983143003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#319783}

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