Update Error Event inside a worker to provide the exact exception value

third_party/WebKit/LayoutTests/fast/workers/resources/error-script.js

+addEventListener("error", function(e) {
+  postMessage({ source: "event listener", value: e.error });

[nhiroki, 2017/04/05 07:38:38]

I'm not sure what we want to check by "source". Is it necessary?

[yiyix, 2017/04/05 09:02:55]

I thought it is like a bonus to test the event source. It is not necessary to
add source as an attribute in this message. I can remove "source" 

+});
+
+throw "testError";