Referrer Policy: Add new policies to URLRequest.

This patch introduces two new referrer policy at the network level in order
to support stripping detail from the referrer header when a redirect
transitions across origins. These policies support both the "reduce referer
granularity" command-line flag, as well as the yet-to-be-implemented
"OriginWhenCrossOrigin" referrer policy specified at [1].



Review URL:

Cr-Commit-Position: refs/heads/master@{#305211}
9 files changed