Add dummy dart:html library for documentation.

lib/html/doc/interface/WheelEvent.dartdoc

Index: lib/html/doc/interface/WheelEvent.dartdoc
diff --git a/lib/html/doc/interface/WheelEvent.dartdoc b/lib/html/doc/interface/WheelEvent.dartdoc
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+// Copyright (c) 2012, 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.
+
+// WARNING:
+//   This file contains documentation that is merged into the real source.
+//   Do not make code changes here.
+
+/// @domName WheelEvent
+interface WheelEvent extends UIEvent {
+
+  /** @domName WheelEvent.altKey */
+  final bool altKey;
+
+  /** @domName WheelEvent.clientX */
+  final int clientX;
+
+  /** @domName WheelEvent.clientY */
+  final int clientY;
+
+  /** @domName WheelEvent.ctrlKey */
+  final bool ctrlKey;
+
+  /** @domName WheelEvent.metaKey */
+  final bool metaKey;
+
+  /** @domName WheelEvent.offsetX */
+  final int offsetX;
+
+  /** @domName WheelEvent.offsetY */
+  final int offsetY;
+
+  /** @domName WheelEvent.screenX */
+  final int screenX;
+
+  /** @domName WheelEvent.screenY */
+  final int screenY;
+
+  /** @domName WheelEvent.shiftKey */
+  final bool shiftKey;
+
+  /** @domName WheelEvent.webkitDirectionInvertedFromDevice */
+  final bool webkitDirectionInvertedFromDevice;
+
+  /** @domName WheelEvent.wheelDelta */
+  final int wheelDelta;
+
+  /** @domName WheelEvent.wheelDeltaX */
+  final int wheelDeltaX;
+
+  /** @domName WheelEvent.wheelDeltaY */
+  final int wheelDeltaY;
+
+  /** @domName WheelEvent.x */
+  final int x;
+
+  /** @domName WheelEvent.y */
+  final int y;
+
+  /** @domName WheelEvent.initWebKitWheelEvent */
+  void initWebKitWheelEvent(int wheelDeltaX, int wheelDeltaY, Window view, int screenX, int screenY, int clientX, int clientY, bool ctrlKey, bool altKey, bool shiftKey, bool metaKey);
+}