Add dummy dart:html library for documentation.

lib/html/doc/interface/HTMLCollection.dart

Index: lib/html/doc/interface/HTMLCollection.dart
diff --git a/lib/html/doc/interface/HTMLCollection.dart b/lib/html/doc/interface/HTMLCollection.dart
new file mode 100644
index 0000000000000000000000000000000000000000..bd198a9e24a7b91516f25492406b329a9e0a94d9
--- /dev/null
+++ b/lib/html/doc/interface/HTMLCollection.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 HTMLCollection
+interface HTMLCollection extends List<Node> {
+
+  /** @domName HTMLCollection.length */
+  final int length;
+
+  /** @domName HTMLCollection.item */
+  Node item(int index);
+
+  /** @domName HTMLCollection.namedItem */
+  Node namedItem(String name);
+}