Apply Referrer-Policy header when following redirects

When a Referrer-Policy header is received during a redirect,
URLRequestJob parses it and updates the referrer and referrer policy on
the request, if necessary.

The Referrer-Policy header is being implemented as an experimental web
platform feature. The experimental web platform feature flag is plumbed
to URLRequestJob via a boolean on URLRequestContext. This flag should be
temporary and only live until the Referrer-Policy feature ships.

Intent to Implement: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/Umj9iVRJM70
Implementation plan: https://docs.google.com/document/d/1SyQhP6Y7BHIQXWL8S1saWqMuar4hoWLGigQuHmizg3g/edit

BUG=619228

Review-Url: https://codereview.chromium.org/2100583002
Cr-Commit-Position: refs/heads/master@{#403017}
19 files changed