DevTools: Fix timeline overview popover sticking at last

third_party/WebKit/Source/devtools/front_end/timeline/TimelineFlameChartDataProvider.js

 /*
  * Copyright (C) 2014 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 972 matching lines @@
    */
   _eventParent(event) {
     return this._entryParent[event[Timeline.TimelineFlameChartDataProvider._indexSymbol]] || null;
   }
 
   /**
    * @param {number} entryIndex
    * @return {?SDK.TracingModel.Event}
    */
   eventByIndex(entryIndex) {
-    return this._entryType(entryIndex) === Timeline.TimelineFlameChartDataProvider.EntryType.Event ?
+    return entryIndex >= 0 && this._entryType(entryIndex) === Timeline.TimelineFlameChartDataProvider.EntryType.Event ?
         /** @type {!SDK.TracingModel.Event} */ (this._entryData[entryIndex]) :
         null;
   }
 
   /**
    * @param {function(!SDK.TracingModel.Event):string} colorForEvent
    */
   setEventColorMapping(colorForEvent) {
     this._colorForEvent = colorForEvent;
   }
 };
 
 Timeline.TimelineFlameChartDataProvider.InstantEventVisibleDurationMs = 0.001;
 Timeline.TimelineFlameChartDataProvider._indexSymbol = Symbol('index');
 
 /** @enum {symbol} */
 Timeline.TimelineFlameChartDataProvider.Events = {
   DataChanged: Symbol('DataChanged')
 };
 
 /** @enum {symbol} */
 Timeline.TimelineFlameChartDataProvider.EntryType = {
   Frame: Symbol('Frame'),
   Event: Symbol('Event'),
   InteractionRecord: Symbol('InteractionRecord'),
   ExtensionEvent: Symbol('ExtensionEvent'),
   Screenshot: Symbol('Screenshot'),
 };