Update tests for crrev.com/223985, Update validation messsage strings for stepMismatch.

BUG=161733
TBR=keishi@chromium.org

Review URL: https://codereview.chromium.org/23531067

git-svn-id: svn://svn.chromium.org/blink/trunk@158008 bbb929c8-8fbe-4397-9dbb-9b2b20218538