DevTools: Show top level event initiator when a child is selected.

third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js

 /*
  * Copyright (C) 2012 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 547 matching lines @@
     }
   }
 
   /**
    * @param {!SDK.TracingModel.Event} event
    * @return {boolean}
    */
   _processEvent(event) {
     var recordTypes = TimelineModel.TimelineModel.RecordType;
     var eventStack = this._eventStack;
-
-    if (!eventStack.length) {
+    if (eventStack.length) {
+      event[TimelineModel.TimelineModel._parentSymbol] = eventStack.peekLast();

[caseq, 2017/03/29 22:08:20]

should we stop pretending and do this in TracingModel?

[alph, 2017/03/29 22:16:57]

Can't do it on the TracingModel level, as we have timeline model events injected
(e.g. JSFrame) that are not present on the lower level.

+    } else {
       if (this._currentTaskLayoutAndRecalcEvents && this._currentTaskLayoutAndRecalcEvents.length) {
         var totalTime = this._currentTaskLayoutAndRecalcEvents.reduce((time, event) => time + event.duration, 0);
         if (totalTime > TimelineModel.TimelineModel.Thresholds.ForcedLayout) {
           for (var e of this._currentTaskLayoutAndRecalcEvents) {
             let timelineData = TimelineModel.TimelineData.forEvent(e);
             timelineData.warning = e.name === recordTypes.Layout ?
                 TimelineModel.TimelineModel.WarningType.ForcedLayout :
                 TimelineModel.TimelineModel.WarningType.ForcedStyle;
           }
         }
@@ skipping 444 matching lines @@
         request = new TimelineModel.TimelineModel.NetworkRequest(e);
         requests.set(id, request);
         if (request.startTime)
           requestsList.push(request);
         else
           zeroStartRequestsList.push(request);
       }
     }
     return zeroStartRequestsList.concat(requestsList);
   }
+
+  /**
+   * @param {!SDK.TracingModel.Event} event
+   * @return {?SDK.TracingModel.Event}
+   */
+  static parentEvent(event) {
+    return event[TimelineModel.TimelineModel._parentSymbol] || null;
+  }
 };
 
+TimelineModel.TimelineModel._parentSymbol = Symbol('parent');
+
 /**
  * @enum {string}
  */
 TimelineModel.TimelineModel.RecordType = {
   Task: 'Task',
   Program: 'Program',
   EventDispatch: 'EventDispatch',
 
   GPUTask: 'GPUTask',
 
@@ skipping 758 matching lines @@
     var data = event[TimelineModel.TimelineData._symbol];
     if (!data) {
       data = new TimelineModel.TimelineData();
       event[TimelineModel.TimelineData._symbol] = data;
     }
     return data;
   }
 };
 
 TimelineModel.TimelineData._symbol = Symbol('timelineData');