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

Source/devtools/front_end/StylesSidebarPane.js

Index: Source/devtools/front_end/StylesSidebarPane.js
diff --git a/Source/devtools/front_end/StylesSidebarPane.js b/Source/devtools/front_end/StylesSidebarPane.js
index c9927ac77bd98ac1130e0bd02035d450ff2fcbbb..0b66b9c2bcc934a4e7f847cd3903f132e4b324af 100644
--- a/Source/devtools/front_end/StylesSidebarPane.js
+++ b/Source/devtools/front_end/StylesSidebarPane.js
@@ -2266,6 +2266,8 @@ WebInspector.StylePropertyTreeElement.prototype = {
          */
         function callback(newStyle)
         {
+            delete this._parentPane._userOperation;
+
             if (!newStyle)
                 return;
 
@@ -2278,8 +2280,6 @@ WebInspector.StylePropertyTreeElement.prototype = {
                 section.pane.dispatchEventToListeners("style property toggled");
 
             this._updatePane();
-
-            delete this._parentPane._userOperation;
         }
 
         this._parentPane._userOperation = true;