Fix a bug that <link rel=prerender> is not parsed on mobile.

This bug was introduced in r165160.
https://codereview.chromium.org/132723002/

Review URL: https://codereview.chromium.org/134833005

git-svn-id: svn://svn.chromium.org/blink/trunk@165734 bbb929c8-8fbe-4397-9dbb-9b2b20218538