WebUI: Fix issue with chrome: and file: links

This is a regression from r228073

BUG=None
TBR=dbeam@chromium.org

Review URL: https://codereview.chromium.org/26477007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228191 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228191