Enable XHR upload progress events for Workers.

LayoutTests/http/tests/xmlhttprequest/workers/resources/upload-onprogress-worker.js

+importScripts("worker-pre.js");
+
+function log(message)
+{
+    postMessage("log " + message);
+}
+
+function onLoad()
+{
+    postMessage("DONE");
+}
+
+function onProgress(e)
+{
+    postMessage("tick " + e.loaded);
+}
+
+function init()
+{
+    try {
+        var xhr = new XMLHttpRequest();
+        xhr.upload.onprogress = onProgress;
+        xhr.onload = onLoad;
+        xhr.open("POST", "../../resources/post-echo.cgi");
+        xhr.send((new Array(100000)).join("aa"));
+    } catch (e) {
+        log("Exception received.");
+    }
+}