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

Source/devtools/front_end/StylesSidebarPane.js

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 1679 matching lines @@
                 this._moveEditorFromSelector(moveDirection);
 
             delete this._parentPane._userOperation;
             this._editingSelectorEnded();
             this._markSelectorMatches();
         }
 
         if (newContent)
             newContent = newContent.trim();
         this._parentPane._userOperation = true;
-        WebInspector.cssModel.addRule(this.pane.node.id, newContent, successCallback.bind(this), this.editingSelectorCancelled.bind(this));
+
+        WebInspector.cssModel.requestViaInspectorStylesheet(this.pane.node, viaInspectorCallback.bind(this));
+
+        /**
+         * @this {WebInspector.BlankStylePropertiesSection}
+         * @param {?WebInspector.CSSStyleSheetHeader} styleSheetHeader
+         */
+        function viaInspectorCallback(styleSheetHeader)
+        {
+            if (!styleSheetHeader) {
+                this.editingSelectorCancelled();
+                return;
+            }
+            WebInspector.cssModel.addRule(styleSheetHeader.id, this.pane.node, newContent, successCallback.bind(this), this.editingSelectorCancelled.bind(this));
+        }
     },
 
     editingSelectorCancelled: function()
     {
         delete this._parentPane._userOperation;
         if (!this.isBlank) {
             WebInspector.StylePropertiesSection.prototype.editingSelectorCancelled.call(this);
             return;
         }
 
@@ skipping 1309 matching lines @@
             return;
         }
 
         var results = this._cssCompletions.startsWith(prefix);
         var selectedIndex = this._cssCompletions.mostUsedOf(results);
         completionsReadyCallback(results, selectedIndex);
     },
 
     __proto__: WebInspector.TextPrompt.prototype
 }