Add dummy dart:html library for documentation.

lib/html/doc/nodoc-src/shared_FactoryProviders.dart

+// 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.
+
+class _EventFactoryProvider {
+  factory Event(String type, [bool canBubble = true,
+                              bool cancelable = true]) => null;
+}
+
+class _MouseEventFactoryProvider {
+  factory MouseEvent(String type, Window view, int detail,
+      int screenX, int screenY, int clientX, int clientY, int button,
+      [bool canBubble = true, bool cancelable = true, bool ctrlKey = false,
+      bool altKey = false, bool shiftKey = false, bool metaKey = false,
+       EventTarget relatedTarget = null]) => null;
+}
+
+class _CSSStyleDeclarationFactoryProvider {
+  factory CSSStyleDeclaration.css(String css) => null;
+  factory CSSStyleDeclaration() => null;
+}
+
+class _DocumentFragmentFactoryProvider {
+  /** @domName Document.createDocumentFragment */
+  factory DocumentFragment() => document.createDocumentFragment();
+  factory DocumentFragment.html(String html) => null;
+  factory DocumentFragment.xml(String xml) => null;
+  factory DocumentFragment.svg(String svg) => null;
+}
+
+class _SVGElementFactoryProvider {
+  factory SVGElement.tag(String tag) => null;
+  factory SVGElement.svg(String svg) => null;
+}
+
+class _SVGSVGElementFactoryProvider {
+  factory SVGSVGElement() => null;
+}