Retry "Replace RenderFullScreen with top layer"

This patch makes the Fullscreen API use the top layer, as per the latest
Fullscreen spec. This retry fixes some tests/expectations.

Previously landed as r165904 and r165710
Codereviews:
https://codereview.chromium.org/134753003/
https://codereview.chromium.org/139743005/

BUG=240576, 246077

Review URL: https://codereview.chromium.org/142653003

git-svn-id: svn://svn.chromium.org/blink/trunk@166114 bbb929c8-8fbe-4397-9dbb-9b2b20218538