Add dummy dart:html library for documentation.

lib/html/doc/interface/AppletElement.dartdoc

+// 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 HTMLAppletElement
+interface AppletElement extends Element {
+
+  /** @domName HTMLAppletElement.align */
+  String align;
+
+  /** @domName HTMLAppletElement.alt */
+  String alt;
+
+  /** @domName HTMLAppletElement.archive */
+  String archive;
+
+  /** @domName HTMLAppletElement.code */
+  String code;
+
+  /** @domName HTMLAppletElement.codeBase */
+  String codeBase;
+
+  /** @domName HTMLAppletElement.height */
+  String height;
+
+  /** @domName HTMLAppletElement.hspace */
+  String hspace;
+
+  /** @domName HTMLAppletElement.name */
+  String name;
+
+  /** @domName HTMLAppletElement.object */
+  String object;
+
+  /** @domName HTMLAppletElement.vspace */
+  String vspace;
+
+  /** @domName HTMLAppletElement.width */
+  String width;
+}