Add dummy dart:html library for documentation.

lib/html/doc/interface/TableCellElement.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 HTMLTableCellElement
+interface TableCellElement extends Element default _Elements {
+
+  TableCellElement();
+
+  /** @domName HTMLTableCellElement.abbr */
+  String abbr;
+
+  /** @domName HTMLTableCellElement.align */
+  String align;
+
+  /** @domName HTMLTableCellElement.axis */
+  String axis;
+
+  /** @domName HTMLTableCellElement.bgColor */
+  String bgColor;
+
+  /** @domName HTMLTableCellElement.cellIndex */
+  final int cellIndex;
+
+  /** @domName HTMLTableCellElement.ch */
+  String ch;
+
+  /** @domName HTMLTableCellElement.chOff */
+  String chOff;
+
+  /** @domName HTMLTableCellElement.colSpan */
+  int colSpan;
+
+  /** @domName HTMLTableCellElement.headers */
+  String headers;
+
+  /** @domName HTMLTableCellElement.height */
+  String height;
+
+  /** @domName HTMLTableCellElement.noWrap */
+  bool noWrap;
+
+  /** @domName HTMLTableCellElement.rowSpan */
+  int rowSpan;
+
+  /** @domName HTMLTableCellElement.scope */
+  String scope;
+
+  /** @domName HTMLTableCellElement.vAlign */
+  String vAlign;
+
+  /** @domName HTMLTableCellElement.width */
+  String width;
+}