DevTools: Fix regression that slows down "Goto Source" dialog

Source/devtools/front_end/ui/ViewportControl.js

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 48 matching lines @@
 
 /**
  * @interface
  */
 WebInspector.ViewportControl.Provider = function()
 {
 }
 
 WebInspector.ViewportControl.Provider.prototype = {
     /**
+     * @param {number} index
+     * @return {number}
+     */
+    fastHeight: function(index) { return 0; },
+
+    /**
      * @return {number}
      */
     itemCount: function() { return 0; },
 
     /**
      * @param {number} index
      * @return {?WebInspector.ViewportElement}
      */
     itemElement: function(index) { return null; }
 }
 
 /**
  * @interface
  */
 WebInspector.ViewportElement = function() { }
 WebInspector.ViewportElement.prototype = {
     willHide: function() { },
 
     wasShown: function() { },
 
     /**
-     * @return {number}
-     */
-    fastHeight: function() { },
-
-    /**
      * @return {!Element}
      */
     element: function() { },
 }
 
 /**
  * @constructor
  * @implements {WebInspector.ViewportElement}
  * @param {!Element} element
- * @param {number} height
  */
-WebInspector.StaticViewportElement = function(element, height)
+WebInspector.StaticViewportElement = function(element)
 {
     this._element = element;
-    this._height = height;
 }
 
 WebInspector.StaticViewportElement.prototype = {
     willHide: function() { },
 
     wasShown: function() { },
 
     /**
-     * @return {number}
-     */
-    fastHeight: function()
-    {
-        return this._height;
-    },
-
-    /**
      * @return {!Element}
      */
     element: function()
     {
         return this._element;
     },
 }
 
 WebInspector.ViewportControl.prototype = {
     /**
@@ skipping 45 matching lines @@
     },
 
     _rebuildCumulativeHeightsIfNeeded: function()
     {
         if (this._cumulativeHeights)
             return;
         var itemCount = this._provider.itemCount();
         if (!itemCount)
             return;
         this._cumulativeHeights = new Int32Array(itemCount);
-        this._cumulativeHeights[0] = this._provider.itemElement(0).fastHeight();
+        this._cumulativeHeights[0] = this._provider.fastHeight(0);
         for (var i = 1; i < itemCount; ++i)
-            this._cumulativeHeights[i] = this._cumulativeHeights[i - 1] + this._provider.itemElement(i).fastHeight();
+            this._cumulativeHeights[i] = this._cumulativeHeights[i - 1] + this._provider.fastHeight(i);
     },
 
     /**
      * @param {number} index
      * @return {number}
      */
     _cachedItemHeight: function(index)
     {
         return index === 0 ? this._cumulativeHeights[0] : this._cumulativeHeights[index] - this._cumulativeHeights[index - 1];
     },
@@ skipping 150 matching lines @@
 
         var visibleFrom = this.element.scrollTop;
         var clientHeight = this.element.clientHeight;
         var shouldStickToBottom = this._stickToBottom && this.element.isScrolledToBottom();
 
         if (this._cumulativeHeights && itemCount !== this._cumulativeHeights.length)
             delete this._cumulativeHeights;
         for (var i = 0; i < this._renderedItems.length; ++i) {
             this._renderedItems[i].willHide();
             // Tolerate 1-pixel error due to double-to-integer rounding errors.
-            if (this._cumulativeHeights && Math.abs(this._cachedItemHeight(this._firstVisibleIndex + i) - this._renderedItems[i].fastHeight()) > 1)
+            if (this._cumulativeHeights && Math.abs(this._cachedItemHeight(this._firstVisibleIndex + i) - this._provider.fastHeight(i + this._firstVisibleIndex)) > 1)
                 delete this._cumulativeHeights;
         }
         this._rebuildCumulativeHeightsIfNeeded();
         if (shouldStickToBottom) {
             this._lastVisibleIndex = itemCount - 1;
             this._firstVisibleIndex = Math.max(Array.prototype.lowerBound.call(this._cumulativeHeights, this._cumulativeHeights[this._cumulativeHeights.length - 1] - clientHeight), 0);
         } else {
             this._firstVisibleIndex = Math.max(Array.prototype.lowerBound.call(this._cumulativeHeights, visibleFrom), 0);
             this._lastVisibleIndex = Math.min(Array.prototype.upperBound.call(this._cumulativeHeights, visibleFrom + clientHeight), itemCount - 1);
         }
@@ skipping 139 matching lines @@
 
     /**
      * @param {number} index
      */
     forceScrollItemToBeLast: function(index)
     {
         this._rebuildCumulativeHeightsIfNeeded();
         this.element.scrollTop = this._cumulativeHeights[index] - this.element.clientHeight;
     }
 }