Add error-event-ready-state.html layout test.

The readyState inside the WebSocket onerror callback should be 3 (CLOSED). This
layout test verifies that.

BUG=

Review URL: https://codereview.chromium.org/133533008

git-svn-id: svn://svn.chromium.org/blink/trunk@167079 bbb929c8-8fbe-4397-9dbb-9b2b20218538