From https://codereview.chromium.org/2483703002/diff/20001/content/renderer/render_frame_impl.cc#newcode3128

> On that note, if you plan to use this on the browser side, it'd be good to have
> a browsertest to verify the feature_policy_header on FrameTreeNode (see the CSP
> and other replication tests in SitePerProcessBrowserTest).  Probably fine if you
> want to add it later though, given that you have end-to-end coverage with your
> layout test.

We should add that test; filing this to make sure it doesn't get forgotten.