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

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

Index: third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js b/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
index d9e3925e16f3239f405a77ba8564a1eb57530692..19fd3a7534b65048fa076c56153c3f42d89df2f8 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
@@ -565,8 +565,9 @@ TimelineModel.TimelineModel = class {
   _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) {
@@ -1031,8 +1032,18 @@ TimelineModel.TimelineModel = class {
     }
     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}
  */