Timeline: remove redundant header from frame statistics

Source/devtools/front_end/timeline/TimelineFrameModel.js

 /*
  * Copyright (C) 2013 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 358 matching lines @@
 ];
 
 WebInspector.TracingTimelineFrameModel.prototype = {
     /**
      * @param {!Array.<!WebInspector.TracingModel.Event>} events
      * @param {string} sessionId
      */
     addTraceEvents: function(events, sessionId)
     {
         this._sessionId = sessionId;
+        if (!events.length)
+            return;
+        if (events[0].startTime < this._minimumRecordTime)
+            this._minimumRecordTime = events[0].startTime;
         for (var i = 0; i < events.length; ++i)
             this._addTraceEvent(events[i]);
     },
 
     /**
      * @param {!WebInspector.TracingModel.Event} event
      */
     _addTraceEvent: function(event)
     {
         var eventNames = WebInspector.TracingTimelineModel.RecordType;
@@ skipping 167 matching lines @@
     /**
      * @param {string} category
      * @param {number} time
      */
     _addTimeForCategory: function(category, time)
     {
         this.timeByCategory[category] = (this.timeByCategory[category] || 0) + time;
         this.cpuTime += time;
     },
 }