Add dummy dart:html library for documentation.

lib/html/doc/interface/CSSRuleList.dart

Index: lib/html/doc/interface/CSSRuleList.dart
diff --git a/lib/html/doc/interface/CSSRuleList.dart b/lib/html/doc/interface/CSSRuleList.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4bab1ff533047919d80c5d62fe03061915911c64
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+++ b/lib/html/doc/interface/CSSRuleList.dart
@@ -0,0 +1,15 @@
+// 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 CSSRuleList
+interface CSSRuleList {
+
+  /** @domName CSSRuleList.length */
+  final int length;
+
+  /** @domName CSSRuleList.item */
+  CSSRule item(int index);
+}