Enable Unprefixed Fullscreen API by default.

Approved Intent to Ship:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/ODzbWn-xRrQ/dhkJzD8-CgAJ

BUG=383813

Change-Id: Ia0b1e681520728c290ce7e1f95388bc27ebf91d0
Reviewed-on: https://chromium-review.googlesource.com/1204595
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589185}
5 files changed