Call notifyAbort when error occurs

notifyAbort will be used to terminate the benchmark in performance tests.
Otherwise, the benchmark stops working, causing timeout.

R=tyoshino@chromium.org

Review URL: https://codereview.appspot.com/173940043

git-svn-id: http://pywebsocket.googlecode.com/svn/trunk@857 4ff78f4a-9131-11de-b045-6380ec9940d4