Also mark the REF "experimental", so that it is tested, and add a test.

Bug: 1053510
Change-Id: I8bac9c8002d20991599a1bf396f28dd9101b0f63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2157988
Reviewed-by: Nicolás Peña Moreno <[email protected]>
Commit-Queue: Steve Kobes <[email protected]>
Cr-Commit-Position: refs/heads/master@{#762442}