DevTools: speed up network scrolling and layout.

Source/devtools/front_end/DataGrid.js

 /*
  * Copyright (C) 2008 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
  *        notice, this list of conditions and the following disclaimer in the
@@ skipping 696 matching lines @@
 
     scrollToLastRow: function()
     {
         this._scrollContainer.scrollTop = this._scrollContainer.scrollHeight - this._scrollContainer.offsetHeight;
     },
 
     _positionResizers: function()
     {
         var headerTableColumns = this._headerTableColumnGroup.children;
         var numColumns = headerTableColumns.length - 1; // Do not process corner column.
-        var left = 0;
+        var left = [];
         var previousResizer = null;
 
+        for (var i = 0; i < numColumns - 1; i++) {
+            // Get the width of the cell in the first (and only) row of the
+            // header table in order to determine the width of the column, since
+            // it is not possible to query a column for its width.
+            left[i] = (left[i-1] || 0) + this.headerTableBody.rows[0].cells[i].offsetWidth;
+        }
+
         // Make n - 1 resizers for n columns.
         for (var i = 0; i < numColumns - 1; i++) {
             var resizer = this.resizers[i];
 
             if (!resizer) {
                 // This is the first call to updateWidth, so the resizers need
                 // to be created.
                 resizer = document.createElement("div");
                 resizer.classList.add("data-grid-resizer");
                 // This resizer is associated with the column to its right.
                 WebInspector.installDragHandle(resizer, this._startResizerDragging.bind(this), this._resizerDragging.bind(this), this._endResizerDragging.bind(this), "col-resize");
                 this.element.appendChild(resizer);
                 this.resizers[i] = resizer;
             }
 
-            // Get the width of the cell in the first (and only) row of the
-            // header table in order to determine the width of the column, since
-            // it is not possible to query a column for its width.
-            left += this.headerTableBody.rows[0].cells[i].offsetWidth;
 
             if (!this._columnsArray[i].hidden) {
                 resizer.style.removeProperty("display");
-                if (resizer._position !== left) {
-                    resizer._position = left;
-                    resizer.style.left = left + "px";
+                if (resizer._position !== left[i]) {
+                    resizer._position = left[i];
+                    resizer.style.left = left[i] + "px";
                 }
                 resizer.leftNeighboringColumnIndex = i;
                 if (previousResizer)
                     previousResizer.rightNeighboringColumnIndex = i;
                 previousResizer = resizer;
             } else {
-                if (previousResizer && previousResizer._position !== left) {
-                    previousResizer._position = left;
-                    previousResizer.style.left = left + "px";
+                if (previousResizer && previousResizer._position !== left[i]) {
+                    previousResizer._position = left[i];
+                    previousResizer.style.left = left[i] + "px";
                 }
-                resizer.style.setProperty("display", "none");
+                if (resizer.style.getPropertyValue("display") !== "none")
+                    resizer.style.setProperty("display", "none");
                 resizer.leftNeighboringColumnIndex = 0;
                 resizer.rightNeighboringColumnIndex = 0;
             }
         }
         if (previousResizer)
             previousResizer.rightNeighboringColumnIndex = numColumns - 1;
     },
 
     addCreationNode: function(hasChildren)
     {
@@ skipping 1044 matching lines @@
 
 WebInspector.CreationDataGridNode.prototype = {
     makeNormal: function()
     {
         delete this.isCreationNode;
         delete this.makeNormal;
     },
 
     __proto__: WebInspector.DataGridNode.prototype
 }