DevTools: fix flame chart on profiler pane

third_party/WebKit/Source/devtools/front_end/perf_ui/FlameChart.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 1008 matching lines @@
     var groups = this._rawTimelineData.groups || [];
     this._visibleLevelOffsets = new Uint32Array(levelCount + 1);
     this._visibleLevels = new Uint16Array(levelCount);
     this._groupOffsets = new Uint32Array(groups.length + 1);
 
     var groupIndex = -1;
     var currentOffset = this._rulerEnabled ? PerfUI.FlameChart.HeaderHeight : 2;
     var visible = true;
     /** @type !Array<{nestingLevel: number, visible: boolean}> */
     var groupStack = [{nestingLevel: -1, visible: true}];
-    var lastGroupLevel = Math.max(levelCount, groups.peekLast().startLevel + 1);
+    var lastGroupLevel = Math.max(levelCount, groups.length ? groups.peekLast().startLevel + 1 : 0);
     for (var level = 0; level < lastGroupLevel; ++level) {
       while (groupIndex < groups.length - 1 && level === groups[groupIndex + 1].startLevel) {
         ++groupIndex;
         var style = groups[groupIndex].style;
         var nextLevel = true;
         while (groupStack.peekLast().nestingLevel >= style.nestingLevel) {
           groupStack.pop();
           nextLevel = false;
         }
         var thisGroupIsVisible =
@@ skipping 489 matching lines @@
   }
 
   /**
    * @override
    * @return {number}
    */
   boundarySpan() {
     return this._maximumBoundaries - this._minimumBoundaries;
   }
 };