Add constructors to all the event classes.

client/html/src/ProgressEventWrappingImplementation.dart

Index: client/html/src/ProgressEventWrappingImplementation.dart
diff --git a/client/html/src/ProgressEventWrappingImplementation.dart b/client/html/src/ProgressEventWrappingImplementation.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f1982b41d1462bc51a8e39c3451cf6573a21359c
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+++ b/client/html/src/ProgressEventWrappingImplementation.dart
@@ -0,0 +1,22 @@
+// 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 ProgressEventWrappingImplementation extends EventWrappingImplementation implements ProgressEvent {
+  ProgressEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory ProgressEventWrappingImplementation(String type, int loaded,
+      [bool canBubble = true, bool cancelable = true,
+      bool lengthComputable = false, int total = 0]) {
+    final e = dom.document.createEvent("ProgressEvent");
+    e.initProgressEvent(type, canBubble, cancelable, lengthComputable, loaded,
+        total);
+    return LevelDom.wrapProgressEvent(e);
+  }
+
+  bool get lengthComputable() => _ptr.lengthComputable;
+
+  int get loaded() => _ptr.loaded;
+
+  int get total() => _ptr.total;
+}