Reapply 169371 "DevTools: defer styles delta calculation to until the end of the task"

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 2248 matching lines @@
     toggleEnabled: function(event)
     {
         var disabled = !event.target.checked;
 
         /**
          * @param {?WebInspector.CSSStyleDeclaration} newStyle
          * @this {WebInspector.StylePropertyTreeElement}
          */
         function callback(newStyle)
         {
+            delete this._parentPane._userOperation;
+
             if (!newStyle)
                 return;
 
             newStyle.parentRule = this.style.parentRule;
             this.style = newStyle;
             this._styleRule.style = newStyle;
 
             var section = this.section();
             if (section && section.pane)
                 section.pane.dispatchEventToListeners("style property toggled");
 
             this._updatePane();
-
-            delete this._parentPane._userOperation;
         }
 
         this._parentPane._userOperation = true;
         this.property.setDisabled(disabled, callback.bind(this));
         event.consume();
     },
 
     onpopulate: function()
     {
         // Only populate once and if this property is a shorthand.
@@ skipping 741 matching lines @@
             return;
         }
 
         var results = this._cssCompletions.startsWith(prefix);
         var selectedIndex = this._cssCompletions.mostUsedOf(results);
         completionsReadyCallback(results, selectedIndex);
     },
 
     __proto__: WebInspector.TextPrompt.prototype
 }