Expose CSSGroupingRule

Source/core/css/CSSGroupingRule.idl

Index: Source/core/css/CSSGroupingRule.idl
diff --git a/Source/core/css/CSSGroupingRule.idl b/Source/core/css/CSSGroupingRule.idl
new file mode 100644
index 0000000000000000000000000000000000000000..c6dbf4ecc75761af0643ed143d89d26e9c9aee00
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+++ b/Source/core/css/CSSGroupingRule.idl
@@ -0,0 +1,11 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// http://dev.w3.org/csswg/cssom/#the-cssgroupingrule-interface
+
+interface CSSGroupingRule : CSSRule {
+    [SameObject] readonly attribute CSSRuleList cssRules;
+    [RaisesException] unsigned long insertRule(DOMString rule, unsigned long index);
+    [RaisesException] void deleteRule(unsigned long index);
+};