Timeline: fix collapse of empty network pane

third_party/WebKit/Source/devtools/front_end/ui_lazy/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 955 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 = UI.FlameChart.DividersBarHeight;
     var visible = true;
     /** @type !Array<{nestingLevel: number, visible: boolean}> */
     var groupStack = [{nestingLevel: -1, visible: true}];
-    for (var level = 0; level < levelCount; ++level) {
+    var lastGroupLevel = Math.max(levelCount, groups.peekLast().startLevel + 1);
+    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 =
             groupIndex >= 0 && this._isGroupCollapsible(groupIndex) ? groups[groupIndex].expanded : true;
         var parentGroupIsVisible = groupStack.peekLast().visible;
         visible = thisGroupIsVisible && parentGroupIsVisible;
         groupStack.push({nestingLevel: style.nestingLevel, visible: visible});
         if (parentGroupIsVisible)
           currentOffset += nextLevel ? 0 : style.padding;
         this._groupOffsets[groupIndex] = currentOffset;
         if (parentGroupIsVisible && !style.shareHeaderLine)
           currentOffset += style.height;
       }
       var isFirstOnLevel = groupIndex >= 0 && level === groups[groupIndex].startLevel;
       var thisLevelIsVisible = visible || isFirstOnLevel && groups[groupIndex].style.useFirstLineForOverview;
-      this._visibleLevels[level] = thisLevelIsVisible;
-      this._visibleLevelOffsets[level] = currentOffset;
+      if (level < levelCount) {
+        this._visibleLevels[level] = thisLevelIsVisible;
+        this._visibleLevelOffsets[level] = currentOffset;
+      }
       if (thisLevelIsVisible || (parentGroupIsVisible && style.shareHeaderLine && isFirstOnLevel))
         currentOffset += this._barHeight;
     }
     if (groupIndex >= 0)
       this._groupOffsets[groupIndex + 1] = currentOffset;
     this._visibleLevelOffsets[level] = currentOffset;
   }
 
   /**
    * @param {number} index
@@ skipping 482 matching lines @@
   }
 
   /**
    * @override
    * @return {number}
    */
   boundarySpan() {
     return this._maximumBoundaries - this._minimumBoundaries;
   }
 };