Add constructors to all the event classes.

client/html/src/WheelEventWrappingImplementation.dart

Index: client/html/src/WheelEventWrappingImplementation.dart
diff --git a/client/html/src/WheelEventWrappingImplementation.dart b/client/html/src/WheelEventWrappingImplementation.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1cd12fd8386c744f74952103110cb80f28e8433c
--- /dev/null
+++ b/client/html/src/WheelEventWrappingImplementation.dart
@@ -0,0 +1,46 @@
+// 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 WheelEventWrappingImplementation extends UIEventWrappingImplementation implements WheelEvent {
+  WheelEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory WheelEventWrappingImplementation(int deltaX, int deltaY, Window view,
+      int screenX, int screenY, int clientX, int clientY, [bool ctrlKey = false,
+      bool altKey = false, bool shiftKey = false, bool metaKey = false]) {
+    final e = dom.document.createEvent("WheelEvent");
+    e.initWheelEvent(deltaX, deltaY, LevelDom.unwrap(view), screenX, screenY,
+        clientX, clientY, ctrlKey, altKey, shiftKey, metaKey);
+    return LevelDom.wrapWheelEvent(e);
+  }
+
+  bool get altKey() => _ptr.altKey;
+
+  int get clientX() => _ptr.clientX;
+
+  int get clientY() => _ptr.clientY;
+
+  bool get ctrlKey() => _ptr.ctrlKey;
+
+  bool get metaKey() => _ptr.metaKey;
+
+  int get offsetX() => _ptr.offsetX;
+
+  int get offsetY() => _ptr.offsetY;
+
+  int get screenX() => _ptr.screenX;
+
+  int get screenY() => _ptr.screenY;
+
+  bool get shiftKey() => _ptr.shiftKey;
+
+  int get wheelDelta() => _ptr.wheelDelta;
+
+  int get wheelDeltaX() => _ptr.wheelDeltaX;
+
+  int get wheelDeltaY() => _ptr.wheelDeltaY;
+
+  int get x() => _ptr.x;
+
+  int get y() => _ptr.y;
+}