In TestRunner::setValueForUser, the *second* argument needs to be a string

BUG=none
R=mkwst@chromium.org

Review URL: https://codereview.chromium.org/166273013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252019 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252019