DevTools: Unify main thread name across vanilla and tracing timeline modes.

Source/devtools/front_end/timeline/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 94 matching lines @@
 
 WebInspector.TimelineModel.Events = {
     RecordAdded: "RecordAdded",
     RecordsCleared: "RecordsCleared",
     RecordingStarted: "RecordingStarted",
     RecordingStopped: "RecordingStopped",
     RecordingProgress: "RecordingProgress",
     RecordFilterChanged: "RecordFilterChanged"
 }
 
+WebInspector.TimelineModel.MainThreadName = "main";
+
 /**
  * @param {!Array.<!WebInspector.TimelineModel.Record>} recordsArray
  * @param {?function(!WebInspector.TimelineModel.Record)|?function(!WebInspector.TimelineModel.Record,number)} preOrderCallback
  * @param {function(!WebInspector.TimelineModel.Record)|function(!WebInspector.TimelineModel.Record,number)=} postOrderCallback
  * @return {boolean}
  */
 WebInspector.TimelineModel.forAllRecords = function(recordsArray, preOrderCallback, postOrderCallback)
 {
     /**
      * @param {!Array.<!WebInspector.TimelineModel.Record>} records
@@ skipping 239 matching lines @@
      * @return {!Array.<!WebInspector.TimelineModel.Record>}
      */
     children: function() { },
 
     /**
      * @return {number}
      */
     startTime: function() { },
 
     /**
-     * @return {string|undefined}
+     * @return {string}
      */
     thread: function() { },
 
     /**
      * @return {number}
      */
     endTime: function() { },
 
     /**
      * @param {number} endTime
@@ skipping 101 matching lines @@
  * @constructor
  */
 WebInspector.TimelineMergingRecordBuffer.prototype = {
     /**
      * @param {string} thread
      * @param {!Array.<!WebInspector.TimelineModel.Record>} records
      * @return {!Array.<!WebInspector.TimelineModel.Record>}
      */
     process: function(thread, records)
     {
-        if (thread) {
+        if (thread !== WebInspector.TimelineModel.MainThreadName) {
             this._backgroundRecordsBuffer = this._backgroundRecordsBuffer.concat(records);
             return [];
         }
         /**
          * @param {!WebInspector.TimelineModel.Record} a
          * @param {!WebInspector.TimelineModel.Record} b
          */
         function recordTimestampComparator(a, b)
         {
             // Never return 0, as the merge function will squash identical entries.
             return a.startTime() < b.startTime() ? -1 : 1;
         }
         var result = this._backgroundRecordsBuffer.mergeOrdered(records, recordTimestampComparator);
         this._backgroundRecordsBuffer = [];
         return result;
     }
 }