DevTools: avoid layout thrashing on Layers panel

third_party/WebKit/Source/devtools/front_end/ui/treeoutline.js

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  *
  * 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 268 matching lines @@
 
         if (nextSelectedElement) {
             nextSelectedElement.reveal();
             nextSelectedElement.select(false, true);
         }
 
         if (handled)
             event.consume(true);
     },
 
+    /**
+     * @param {!TreeElement} treeElement
+     */
+    _deferredScrollIntoView: function(treeElement)
+    {
+        if (!this._treeElementToScrollIntoView)
+            this.element.window().requestAnimationFrame(deferredScrollIntoView.bind(this));
+        this._treeElementToScrollIntoView = treeElement;
+        /**
+         * @this {TreeOutline}
+         */
+        function deferredScrollIntoView()
+        {
+            var treeElement = this._treeElementToScrollIntoView;
+            delete this._treeElementToScrollIntoView;
+            if (treeElement.treeOutline !== this || !treeElement.listItemElement)

[pfeldman, 2015/11/20 22:48:52]

nuke those

+                return;
+            treeElement.listItemElement.scrollIntoViewIfNeeded();
+            treeElement.onreveal();
+        }
+    },
+
     __proto__: WebInspector.Object.prototype
 }
 
 /**
  * @constructor
  * @extends {TreeOutline}
  * @param {string=} className
  */
 function TreeOutlineInShadow(className)
 {
@@ skipping 555 matching lines @@
 
     reveal: function()
     {
         var currentAncestor = this.parent;
         while (currentAncestor && !currentAncestor.root) {
             if (!currentAncestor.expanded)
                 currentAncestor.expand();
             currentAncestor = currentAncestor.parent;
         }
 
+        this.treeOutline._deferredScrollIntoView(this);
+    },
+
+    _deferredScrollIntoView: function()

[pfeldman, 2015/11/20 22:48:52]

unused

+    {
         this.listItemElement.scrollIntoViewIfNeeded();
-
-        this.onreveal();

[pfeldman, 2015/11/20 22:48:52]

I think you want it there synchronously.

     },
 
     /**
      * @return {boolean}
      */
     revealed: function()
     {
         var currentAncestor = this.parent;
         while (currentAncestor && !currentAncestor.root) {
             if (!currentAncestor.expanded)
@@ skipping 216 matching lines @@
     isEventWithinDisclosureTriangle: function(event)
     {
         // FIXME: We should not use getComputedStyle(). For that we need to get rid of using ::before for disclosure triangle. (http://webk.it/74446)
         var paddingLeftValue = window.getComputedStyle(this._listItemNode).paddingLeft;
         console.assert(paddingLeftValue.endsWith("px"));
         var computedLeftPadding = parseFloat(paddingLeftValue);
         var left = this._listItemNode.totalOffsetLeft() + computedLeftPadding;
         return event.pageX >= left && event.pageX <= left + TreeElement._ArrowToggleWidth && this._expandable;
     }
 }