Fix referrerPolicy IDL attribute spelling

In the grand tradition of trivial HTTP-referrer-related misspellings
that haunt the web forever, I miscapitalized the referrerPolicy IDL
attribute. This CL fixes the mistake for compatibility with Firefox and
the spec (see for example
https://html.spec.whatwg.org/multipage/semantics.html#the-a-element).

BUG=628718

Review-Url: https://codereview.chromium.org/2150393003
Cr-Commit-Position: refs/heads/master@{#406311}
8 files changed