DevTools: update group-by combobox upon tree view change in timeline aggregated details.

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

Index: third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
index 37e7ff121ec87cb141a3fbfb1ac9558ae2a4e757..dc07c7f3a2f0e7a8e7e69c53dbb29a1b632a9097 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
@@ -631,6 +631,7 @@ Timeline.AggregatedTimelineTreeView = class extends Timeline.TimelineTreeView {
     super();
     this._groupBySetting =
         Common.settings.createSetting('timelineTreeGroupBy', Timeline.AggregatedTimelineTreeView.GroupBy.None);
+    this._groupByCombobox = new UI.ToolbarComboBox(this._onGroupByChanged.bind(this));
     this.init(filters);
     this._stackView = new Timeline.TimelineStackView(this);
     this._stackView.addEventListener(
@@ -639,6 +640,16 @@ Timeline.AggregatedTimelineTreeView = class extends Timeline.TimelineTreeView {
 
   /**
    * @override
+   */
+  wasShown() {
+    var groupById = this._groupBySetting.get();
+    var option = this._groupByCombobox.options().find(option => option.value === groupById);
+    if (option)
+      this._groupByCombobox.select(option);
+  }
+
+  /**
+   * @override
    * @param {!Timeline.TimelineSelection} selection
    */
   updateContents(selection) {
@@ -712,7 +723,6 @@ Timeline.AggregatedTimelineTreeView = class extends Timeline.TimelineTreeView {
    */
   populateToolbar(toolbar) {
     super.populateToolbar(toolbar);
-    this._groupByCombobox = new UI.ToolbarComboBox(this._onGroupByChanged.bind(this));
     /**
      * @param {string} name
      * @param {string} id