DevTools: [SSP] Implement adding new rule in user stylesheet

LayoutTests/inspector/elements/styles/styles-add-new-rule.html

Index: LayoutTests/inspector/elements/styles/styles-add-new-rule.html
diff --git a/LayoutTests/inspector/elements/styles/styles-add-new-rule.html b/LayoutTests/inspector/elements/styles/styles-add-new-rule.html
index 856750b3821e3de6c727d703c47860ca483711d7..f486306c9dd10452b6bf9e8b29f413d342eab7f5 100644
--- a/LayoutTests/inspector/elements/styles/styles-add-new-rule.html
+++ b/LayoutTests/inspector/elements/styles/styles-add-new-rule.html
@@ -40,8 +40,12 @@ function test()
     function step3()
     {
         // Click "Add new rule".
-        document.getElementById("add-style-button-test-id").click();
-        InspectorTest.selectNodeAndWaitForStyles("inspected", step4);
+        InspectorTest.addNewRule(null, onRuleAdded);
+
+        function onRuleAdded()
+        {
+            InspectorTest.selectNodeAndWaitForStyles("inspected", step4);
+        }
     }
 
     function step4()