[referrer-policy-tests] Update referrer-policy tests to test the `referrerpolicy` attribute (#2550)

This PR does the following things:
- changes the referrer-policy attribute value from `referrer` to `referrerpolicy` to match recent changes in the spec
- updates the common referrer-policy test case code to support the `referrerpolicy` attribute for `img` and `iframe`
- generates tests for the range of `referrerpolicy` attribute values and supported elements

Chrome Canary passes these new tests for the `referrerpolicy` attribute when run with --enable-experimental-web-platform-features to enable the attribute.

This is my first time working on this repo so please let me know if I've done anything silly!

cc @jeisinger @franziskuskiefer

View on GitHub: https://github.com/w3c/web-platform-tests/pull/2550

Received on Tuesday, 2 February 2016 03:13:02 UTC