Make CSSHostRule.addRule() / deleteRule() arguments mandatory

LayoutTests/fast/dom/shadow/css-hostrule-api.html

Index: LayoutTests/fast/dom/shadow/css-hostrule-api.html
diff --git a/LayoutTests/fast/dom/shadow/css-hostrule-api.html b/LayoutTests/fast/dom/shadow/css-hostrule-api.html
index 06d278695724470a2605267ab749002254b98e2e..2813f82793480a406ccac2575db48ddb1d520791 100644
--- a/LayoutTests/fast/dom/shadow/css-hostrule-api.html
+++ b/LayoutTests/fast/dom/shadow/css-hostrule-api.html
@@ -42,6 +42,15 @@ shouldBe("hostRule.cssRules.length", '1');
 shouldBe("hostRule.cssText", '"@host { \\n  div { border-color: blue; }\\n}"');
 shouldBe("hostRule.cssRules[0].cssText", '"div { border-color: blue; }"');
 
+debug("Error cases");
+shouldBe("hostRule.cssRules.length", '1');
+shouldThrow("hostRule.insertRule('#host { border-color: green; }')", "'TypeError: Not enough arguments'");
+shouldBe("hostRule.cssRules.length", '1');
+shouldThrow("hostRule.insertRule()", "'TypeError: Not enough arguments'");
+shouldBe("hostRule.cssRules.length", '1');
+shouldThrow("hostRule.deleteRule()", "'TypeError: Not enough arguments'");
+shouldBe("hostRule.cssRules.length", '1');
+
 </script>
 <script src="../../js/resources/js-test-post.js"></script>
 </html>