DevTools: Optimize events overview drawing performance

Source/devtools/front_end/ui_lazy/TimelineOverviewPane.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 37 matching lines @@
     this._overviewGrid.setResizeEnabled(false);
     this._overviewGrid.addEventListener(WebInspector.OverviewGrid.Events.WindowChanged, this._onWindowChanged, this);
     this._overviewGrid.addEventListener(WebInspector.OverviewGrid.Events.Click, this._onClick, this);
     this._overviewControls = [];
     this._markers = new Map();
 
     this._popoverHelper = new WebInspector.PopoverHelper(this.contentElement, this._getPopoverAnchor.bind(this), this._showPopover.bind(this), this._onHidePopover.bind(this));
     this._popoverHelper.setTimeout(0);
 
     this._cursorEnabled = false;
+    this._lastWidth = 0;
 }
 
 WebInspector.TimelineOverviewPane.Events = {
     WindowChanged: "WindowChanged"
 };
 
 WebInspector.TimelineOverviewPane.prototype = {
     /**
      * @param {!Element} element
      * @param {!Event} event
@@ skipping 69 matching lines @@
     wasShown: function()
     {
         this.update();
     },
 
     /**
      * @override
      */
     onResize: function()
     {
+        var width = this.element.offsetWidth;
+        if (width === this._lastWidth)
+            return;
+        this._lastWidth = width;
         this.update();
     },
 
     /**
      * @param {!Array.<!WebInspector.TimelineOverview>} overviewControls
      */
     setOverviewControls: function(overviewControls)
     {
         for (var i = 0; i < this._overviewControls.length; ++i)
             this._overviewControls[i].dispose();
@@ skipping 416 matching lines @@
     },
 
     resetCanvas: function()
     {
         this._canvas.width = this.element.clientWidth * window.devicePixelRatio;
         this._canvas.height = this.element.clientHeight * window.devicePixelRatio;
     },
 
     __proto__: WebInspector.VBox.prototype
 }