Remove Chromium plumbing for fixed-position-creates-stacking-context
This is a no-op since over a month ago:
https://codereview.chromium.org/
206463009/
So it's probably safe to remove the Chromium code which plumbs
this preference around before Blink drops it on the floor.
After this lands, WebSettings::setFixedPositionCreatesStackingContext
can be removed entirely.
BUG=354688
Review URL: https://codereview.chromium.org/
289973008
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273045 0039d316-1c4b-4281-b951-d872f2087c98