Timeline: fix NPE when hovering over Interactions strip

third_party/WebKit/Source/devtools/front_end/timeline/TimelineFlameChart.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 479 matching lines @@
     }
     return element;
   }
 
   /**
    * @override
    * @param {number} entryIndex
    */
   highlightEntry(entryIndex) {
     SDK.DOMModel.hideDOMNodeHighlight();
+    if (this._entryType(entryIndex) !== Timeline.TimelineFlameChartEntryType.Event)
+      return;
     var event = /** @type {!SDK.TracingModel.Event} */ (this._entryData[entryIndex]);
-    if (!event)
-      return;
     var target = this._model.targetByEvent(event);
     if (!target)
       return;
     var timelineData = TimelineModel.TimelineData.forEvent(event);
     var backendNodeId = timelineData.backendNodeId;
     if (!backendNodeId)
       return;
     new SDK.DeferredDOMNode(target, backendNodeId).highlight();
   }
 
@@ skipping 301 matching lines @@
    * @return {boolean}
    */
   _isVisible(event) {
     return this._filters.every(function(filter) {
       return filter.accept(event);
     });
   }
 };
 
 Timeline.TimelineFlameChartDataProvider.InstantEventVisibleDurationMs = 0.001;