Revert of Reland r165710 "Replace RenderFullScreen with top layer" (https://codereview.chromium.org/134753003/)

Reason for revert:
Looks like it's causing failures on:
virtual/android/fullscreen/anonymous-block-merge-crash.html
fullscreen/anonymous-block-merge-crash.html
virtual/android/fullscreen/full-screen-iframe-legacy.html
plugin-document-back-forward.html

See:
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux/builds/26047
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20(dbg)/builds/17197
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.6%20%28dbg%29/builds/11804

Original issue's description:
> Reland r165710 "Replace RenderFullScreen with top layer"
> 
> It broke browser_test OutOfProcessPPAPITest.Fullscreen by tripping an
> assert reached by calling pluginWidget in HTMLPluginElement::detach
> which causes a layout. The solution is to get the existing widget
> without causing a layout.
> 
> Original code review: https://codereview.chromium.org/139743005/
> 
> BUG=240576, 246077
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165904

TBR=esprehn@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=240576, 246077

Review URL: https://codereview.chromium.org/132333018

git-svn-id: svn://svn.chromium.org/blink/trunk@165928 bbb929c8-8fbe-4397-9dbb-9b2b20218538