DevTools: Add grouping by Activity to Timeline treeview.

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

Index: third_party/WebKit/Source/devtools/front_end/timeline/TimelineProfileTree.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineProfileTree.js b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineProfileTree.js
index 6eeb31caca44b9afb9b1a4cd27fde8fd3adc8a9f..2d7a87cdb18eeee461cd02146bfe4d933d6551aa 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineProfileTree.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineProfileTree.js
@@ -232,6 +232,7 @@ WebInspector.TimelineAggregator = function(categoryMapper)
  */
 WebInspector.TimelineAggregator.GroupBy = {
     None: "None",
+    EventName: "EventName",
     Category: "Category",
     Domain: "Domain",
     Subdomain: "Subdomain",
@@ -336,6 +337,7 @@ WebInspector.TimelineAggregator.prototype = {
 
         switch (groupBy) {
         case WebInspector.TimelineAggregator.GroupBy.None: return null;
+        case WebInspector.TimelineAggregator.GroupBy.EventName: return node => node.event.name;

[alph, 2016/05/26 07:23:20]

Can event be null? There's a check on the next line.

         case WebInspector.TimelineAggregator.GroupBy.Category: return node => node.event ? this._categoryMapper(node.event) : "";
         case WebInspector.TimelineAggregator.GroupBy.Subdomain: return groupByDomain.bind(null, false);
         case WebInspector.TimelineAggregator.GroupBy.Domain: return groupByDomain.bind(null, true);