Add constructors to all the event classes.

client/html/src/XMLHttpRequestProgressEventWrappingImplementation.dart

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class XMLHttpRequestProgressEventWrappingImplementation extends ProgressEventWrappingImplementation implements XMLHttpRequestProgressEvent {
+  XMLHttpRequestProgressEventWrappingImplementation._wrap(ptr) : super._wrap(ptr) {}
+
+  factory XMLHttpRequestProgressEventWrappingImplementation(String type,
+      int loaded, [bool canBubble = false, bool cancelable = false,
+      bool lengthComputable = false, int total = 0]) {
+    var e = dom.document.createEvent("XMLHttpRequestProgressEvent");
+    e.initProgressEvent(type, canBubble, cancelable, lengthComputable, loaded,
+        total);
+    return LevelDom.wrapProgressEvent(e);
+  }
+
+  int get position() { return _ptr.position; }
+
+  int get totalSize() { return _ptr.totalSize; }
+}