html5-full-render.html test uses substring but meant substr
https://bugs.webkit.org/show_bug.cgi?id=99495

Patch by Elliott Sprehn <esprehn@chromium.org> on 2012-10-16
Reviewed by Adam Barth.

This test intended to chunk up the HTML5 spec into chunks of 500k chars, but used
substring(to,from) instead of substr(from,length) so it actually loaded 5x more
content than was in the HTML5 spec.

* Parser/html5-full-render.html:

git-svn-id: svn://svn.chromium.org/blink/trunk@131553 bbb929c8-8fbe-4397-9dbb-9b2b20218538