Add dummy dart:html library for documentation.

lib/html/doc/interface/CSSMediaRule.dart

Index: lib/html/doc/interface/CSSMediaRule.dart
diff --git a/lib/html/doc/interface/CSSMediaRule.dart b/lib/html/doc/interface/CSSMediaRule.dart
new file mode 100644
index 0000000000000000000000000000000000000000..bb932b4eb4006c7c93ed00a7a0cdf8273bf5b4fc
--- /dev/null
+++ b/lib/html/doc/interface/CSSMediaRule.dart
@@ -0,0 +1,21 @@
+// 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 CSSMediaRule
+interface CSSMediaRule extends CSSRule {
+
+  /** @domName CSSMediaRule.cssRules */
+  final CSSRuleList cssRules;
+
+  /** @domName CSSMediaRule.media */
+  final MediaList media;
+
+  /** @domName CSSMediaRule.deleteRule */
+  void deleteRule(int index);
+
+  /** @domName CSSMediaRule.insertRule */
+  int insertRule(String rule, int index);
+}