Headless utility classes for making deterministic protocol handlers

In follow on patches I hope to wire up a URLFetcher backending on
URLRequestHttpJob and adding a --deterministic-network-fetch option
to headless_shell

BUG=546953

Review-Url: https://codereview.chromium.org/2260793002
Cr-Commit-Position: refs/heads/master@{#413130}
19 files changed