Add dummy dart:html library for documentation.

lib/html/doc/interface/HTMLOptionsCollection.dart

Index: lib/html/doc/interface/HTMLOptionsCollection.dart
diff --git a/lib/html/doc/interface/HTMLOptionsCollection.dart b/lib/html/doc/interface/HTMLOptionsCollection.dart
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index 0000000000000000000000000000000000000000..fb9f5147c1eb472df1af5c255bf754d2236ea285
--- /dev/null
+++ b/lib/html/doc/interface/HTMLOptionsCollection.dart
@@ -0,0 +1,18 @@
+// 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: Do not edit - generated code.
+
+/// @domName HTMLOptionsCollection
+interface HTMLOptionsCollection extends HTMLCollection {
+
+  /** @domName HTMLOptionsCollection.length */
+  int length;
+
+  /** @domName HTMLOptionsCollection.selectedIndex */
+  int selectedIndex;
+
+  /** @domName HTMLOptionsCollection.remove */
+  void remove(int index);
+}