Add dummy dart:html library for documentation.

lib/html/doc/interface/ImageElement.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 HTMLImageElement
+interface ImageElement extends Element default _Elements {
+
+  ImageElement([String src, int height, int width]);
+
+  /** @domName HTMLImageElement.align */
+  String align;
+
+  /** @domName HTMLImageElement.alt */
+  String alt;
+
+  /** @domName HTMLImageElement.border */
+  String border;
+
+  /** @domName HTMLImageElement.complete */
+  final bool complete;
+
+  /** @domName HTMLImageElement.crossOrigin */
+  String crossOrigin;
+
+  /** @domName HTMLImageElement.height */
+  int height;
+
+  /** @domName HTMLImageElement.hspace */
+  int hspace;
+
+  /** @domName HTMLImageElement.isMap */
+  bool isMap;
+
+  /** @domName HTMLImageElement.longDesc */
+  String longDesc;
+
+  /** @domName HTMLImageElement.lowsrc */
+  String lowsrc;
+
+  /** @domName HTMLImageElement.name */
+  String name;
+
+  /** @domName HTMLImageElement.naturalHeight */
+  final int naturalHeight;
+
+  /** @domName HTMLImageElement.naturalWidth */
+  final int naturalWidth;
+
+  /** @domName HTMLImageElement.src */
+  String src;
+
+  /** @domName HTMLImageElement.useMap */
+  String useMap;
+
+  /** @domName HTMLImageElement.vspace */
+  int vspace;
+
+  /** @domName HTMLImageElement.width */
+  int width;
+
+  /** @domName HTMLImageElement.x */
+  final int x;
+
+  /** @domName HTMLImageElement.y */
+  final int y;
+}