Revert "Retry "Replace RenderFullScreen with top layer""

This reverts commit 9877946002a47509b8f737b756d5589812ec375c.

Revert "Auto-rebaseline for r166304"

This reverts commit ff6adb9065a035cb3604f067021da882544e5a93.

Revert "Mark full-screen-video-has-backdrop.html as flaky."

This reverts commit 850bb332da7a9bbdba68d91ecd9e1cf68abea612.

The change apparently breaks setAttribute behavior for plugins, though
there is not an easy repro test case yet.

BUG=240576,246077
TBR=hidehiko,esprehn
NOTRY=true
NOTREECHECKS=true

Review URL: https://codereview.chromium.org/142703011

git-svn-id: svn://svn.chromium.org/blink/trunk@166394 bbb929c8-8fbe-4397-9dbb-9b2b20218538