DevTools: Split creating inspector stylesheet and adding a new rule into stylesheet in protocol.

LayoutTests/inspector/elements/styles/edit-inspector-stylesheet.html

Index: LayoutTests/inspector/elements/styles/edit-inspector-stylesheet.html
diff --git a/LayoutTests/inspector/elements/styles/edit-inspector-stylesheet.html b/LayoutTests/inspector/elements/styles/edit-inspector-stylesheet.html
index 1890c0e351973db6cf671292750dd507f082001e..7b07fdfcfd920202e24349bdb485158e254fc626 100644
--- a/LayoutTests/inspector/elements/styles/edit-inspector-stylesheet.html
+++ b/LayoutTests/inspector/elements/styles/edit-inspector-stylesheet.html
@@ -14,24 +14,13 @@ function test()
 
     function step1(node)
     {
-        WebInspector.cssModel.addRule(node.id, "#inspected", successCallback, failureCallback);
-
-        function successCallback()
-        {
-            InspectorTest.waitForStyles("inspected", stylesReceived, true);
-        }
+        InspectorTest.addNewRule("#inspected", stylesReceived);
 
         function stylesReceived()
         {
             // UISourceCode.prototype.addRevision() must finish before step2 is called.
             InspectorTest.showScriptSource("inspector-stylesheet", step2);
         }
-
-        function failureCallback()
-        {
-            InspectorTest.addResult("Failed to add rule.");
-            InspectorTest.completeTest();
-        }
     }
 
     function step2(sourceFrame)