Revert r166476 that broke prerender of large number of pages.

I'm not yet sure why, but r166476 broke rendering results of large
number of pages when prerendered, e.g.
https://www.kymmis.com/

Note that this revert will instead break some other pages like
http://answers.yahoo.com/question/index?qid=20100118183228AAfOKmD
however # of affected pages is a lot smaller than not reverting,
so let me revert it first and take a further look.

BUG=340987

Review URL: https://codereview.chromium.org/153973004

git-svn-id: svn://svn.chromium.org/blink/trunk@166817 bbb929c8-8fbe-4397-9dbb-9b2b20218538