Add dummy dart:html library for documentation.

lib/html/doc/interface/IFrameElement.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 HTMLIFrameElement
+interface IFrameElement extends Element default _Elements {
+
+  IFrameElement();
+
+  /** @domName HTMLIFrameElement.align */
+  String align;
+
+  /** @domName HTMLIFrameElement.contentWindow */
+  final Window contentWindow;
+
+  /** @domName HTMLIFrameElement.frameBorder */
+  String frameBorder;
+
+  /** @domName HTMLIFrameElement.height */
+  String height;
+
+  /** @domName HTMLIFrameElement.longDesc */
+  String longDesc;
+
+  /** @domName HTMLIFrameElement.marginHeight */
+  String marginHeight;
+
+  /** @domName HTMLIFrameElement.marginWidth */
+  String marginWidth;
+
+  /** @domName HTMLIFrameElement.name */
+  String name;
+
+  /** @domName HTMLIFrameElement.sandbox */
+  String sandbox;
+
+  /** @domName HTMLIFrameElement.scrolling */
+  String scrolling;
+
+  /** @domName HTMLIFrameElement.src */
+  String src;
+
+  /** @domName HTMLIFrameElement.srcdoc */
+  String srcdoc;
+
+  /** @domName HTMLIFrameElement.width */
+  String width;
+
+  /** @domName HTMLIFrameElement.getSVGDocument */
+  SVGDocument getSVGDocument();
+}