Add 'self.onerror' to Worker tests.

LayoutTests/http/tests/workers/resources/worker-importscripts-onerror-crossorigin.js

+self.onerror = function (message, url, line, column) {
+    postMessage({ 'message': message, 'url': url, 'line': line, 'column': column });

[do-not-use, 2013/07/25 08:08:14]

Might be nice to use the same naming as in ErrorEvent for consistency, what do
you think?
(http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#e...)

[Mike West, 2013/07/25 08:29:01]

I can do that.

Honestly, I'd prefer to rename the ErrorEvent properties, as they're already
internally inconsistent (lineno (!!) vs column, for instance). :)

+};
+
 importScripts('http://localhost:8000/workers/resources/worker-importScripts-throw.js');