Make img referrerpolicy attribute runtime-enabled

This is a follow-up to https://codereview.chromium.org/1291613010/ where
I forgot to implement the referrerpolicy attribute for img tags as a
runtime-enabled feature.

BUG=490608

Review URL: https://codereview.chromium.org/1302403005

git-svn-id: svn://svn.chromium.org/blink/trunk@201000 bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed
tree: 07bf25b2fffb9cd095d53834c33057183888de0f
  1. third_party/