Here is a summary of hopefully everything it implements:
- Extensions code gets forwarded ~everything
- Header rewriting:
  - Stripping referrers (#838906)
  - Adding headers or rewriting URLs to force google or youtube safe search, based on prefs [no bug for port yet]
  - Adding some sort of google apps related header, based on a pref [no bug for port yet]
- Removal of variations headers on redirects (see #794644 for context), [no bug
  for port yet]
- DomainReliabilityMonitor (#840386)
- Cookie policy (#803452, #789632); including OnCanEnablePrivacyMode
- Also reporting policy, which seems to rely partly on cookie policy, but also has its own thing. [no bug for port yet]
- Which cookies were sent to this URL UI --- #789636
- Policy for file:///. Presumably we won't want network service to handle file:/// at all, due to sandbox,
  but the support in browser should probably implement the same policies. [no bug for port yet]
- OnAreExperimentalCookieFeaturesEnabled --- just a bool from a switch [no bug for port yet]
- Byte transfer metrics:
  - TaskManagerInterface::OnRawBytesRead (and Sent); which also uses content::ResourceRequestInfo::ForRequest(net::URLRequest* request)
    to associate with child and "route_id"
  - data_usage::DataUseAggregator: also looks up LoadTimingInfo for the request, and things like
    request->site_for_cookies()
- Stats & co:
  - RecordNetworkErrorHistograms records Net.HttpRequestCompletionErrorCodes and
    Net.HttpRequestCompletionErrorCodes.MainFrame (based on LOAD_MAIN_FRAME_DEPRECATED).
    This can probably just be in net/?
  - OnCancelURLWithPolicyViolatingReferrerHandler does a DumpWithoutCrashing and adds to another
    Net. histogram

With respect to file policy, looks like the servificied implementation does delegate to it --- via ChromeContentBrowserClient, https://cs.chromium.org/chromium/src/chrome/browser/chrome_content_browser_client.cc?rcl=d6bb2dcc13ac5d402d5f3bbcf8106cd3f2c7f1f0&l=1687, invoked from:

https://cs.chromium.org/chromium/src/content/browser/file_url_loader_factory.cc?rcl=d6bb2dcc13ac5d402d5f3bbcf8106cd3f2c7f1f0&l=146

Hmm, I am not sure OnAreExperimentalCookieFeaturesEnabled is actually used any more, might be able to just excise. 

All blocked bugs resolved.  Resolving Fixed.