diff -r 000000000000 -r 6474c204b198 dom/workers/test/errorwarning_worker.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/workers/test/errorwarning_worker.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,42 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+function errorHandler() {
+  postMessage({ type: 'error' });
+}
+
+onmessage = function(event) {
+  if (event.data.errors) {
+    try {
+      // This is an error:
+      postMessage({ type: 'ignore', value: b.aaa });
+    } catch(e) {
+      errorHandler();
+    }
+  } else {
+    var a = {};
+    // This is a warning:
+    postMessage({ type: 'ignore', value: a.foo });
+  }
+
+  if (event.data.loop != 0) {
+    var worker = new Worker('errorwarning_worker.js');
+    worker.onerror = errorHandler;
+    worker.postMessage({ loop: event.data.loop - 1, errors: event.data.errors });
+
+    worker.onmessage = function(e) {
+      postMessage(e.data);
+    }
+
+  } else {
+    postMessage({ type: 'finish' });
+  }
+}
+
+onerror = errorHandler;
+onerror = onerror;
+if (!onerror || onerror != onerror) {
+  throw "onerror wasn't set properly";
+}