Add constructors to all the event classes.

client/html/src/MouseEventWrappingImplementation.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 MouseEventWrappingImplementation extends UIEventWrappingImplementation implements MouseEvent {
+  MouseEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory MouseEventWrappingImplementation(String type, Window view, int detail,
+      int screenX, int screenY, int clientX, int clientY, int button,
+      [bool canBubble = true, bool cancelable = true, bool ctrlKey = false,
+      bool altKey = false, bool shiftKey = false, bool metaKey = false,
+      EventTarget relatedTarget = null]) {
+    final e = dom.document.createEvent("MouseEvent");
+    e.initMouseEvent(type, canBubble, cancelable, LevelDom.unwrap(view), detail,
+        screenX, screenY, clientX, clientY, ctrlKey, altKey, shiftKey, metaKey,
+        button, LevelDom.unwrap(relatedTarget));
+    return LevelDom.wrapMouseEvent(e);
+  }
+
+  bool get altKey() => _ptr.altKey;
+
+  int get button() => _ptr.button;
+
+  int get clientX() => _ptr.clientX;
+
+  int get clientY() => _ptr.clientY;
+
+  bool get ctrlKey() => _ptr.ctrlKey;
+
+  Node get fromElement() => LevelDom.wrapNode(_ptr.fromElement);
+
+  bool get metaKey() => _ptr.metaKey;
+
+  int get offsetX() => _ptr.offsetX;
+
+  int get offsetY() => _ptr.offsetY;
+
+  EventTarget get relatedTarget() => LevelDom.wrapEventTarget(_ptr.relatedTarget);
+
+  int get screenX() => _ptr.screenX;
+
+  int get screenY() => _ptr.screenY;
+
+  bool get shiftKey() => _ptr.shiftKey;
+
+  Node get toElement() => LevelDom.wrapNode(_ptr.toElement);
+
+  int get x() => _ptr.x;
+
+  int get y() => _ptr.y;
+}