Initialize min/max record time to 0 instead of -1 or null

Source/devtools/front_end/timeline/TracingModel.js

 /*
  * Copyright 2014 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /**
  * @constructor
  * @extends {WebInspector.TargetAwareObject}
  */
@@ skipping 146 matching lines @@
         this._active = false;
         if (!this._pendingStopCallback)
             return;
         this._pendingStopCallback();
         this._pendingStopCallback = null;
     },
 
     reset: function()
     {
         this._processById = {};
-        this._minimumRecordTime = null;
-        this._maximumRecordTime = null;
+        this._minimumRecordTime = 0;
+        this._maximumRecordTime = 0;
         this._sessionId = null;
         this._devtoolsMetadataEvents = [];
     },
 
     /**
       * @param {!WebInspector.TracingModel.EventPayload} payload
       */
     _addEvent: function(payload)
     {
         var process = this._processById[payload.pid];
@@ skipping 32 matching lines @@
         case WebInspector.TracingModel.MetadataEvent.ThreadSortIndex:
             thread._setSortIndex(payload.args["sort_index"]);
             break;
         case WebInspector.TracingModel.MetadataEvent.ThreadName:
             thread._setName(payload.args["name"]);
             break;
         }
     },
 
     /**
-     * @return {?number}
+     * @return {number}
      */
     minimumRecordTime: function()
     {
         return this._minimumRecordTime;
     },
 
     /**
-     * @return {?number}
+     * @return {number}
      */
     maximumRecordTime: function()
     {
         return this._maximumRecordTime;
     },
 
     /**
      * @return {!Array.<!WebInspector.TracingModel.Process>}
      */
     sortedProcesses: function()
@@ skipping 308 matching lines @@
     dataCollected: function(data)
     {
         this._tracingModel._eventsCollected(data);
     },
 
     tracingComplete: function()
     {
         this._tracingModel._tracingComplete();
     }
 }