Do not run the references when a test crashes or times out.

If the actual test in a reftest crashes or times out, we probably shouldn't
bother executing the reference as well, since we have nothing
to compare it to, and the test failed regardless. This can save
a bunch of execution time and avoid some confusion.

R=ojan@chromium.org, abarth@chromium.org, peter@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/23224013

git-svn-id: svn://svn.chromium.org/blink/trunk@156409 bbb929c8-8fbe-4397-9dbb-9b2b20218538