Use monotonic clock instead of currentTimeMillis

Reviewed By: javache

Differential Revision: D3115208

fb-gh-sync-id: c0fef5a162ab023d55736b38c51c87b8759f089d
fbshipit-source-id: c0fef5a162ab023d55736b38c51c87b8759f089d

Libraries/Utilities/PerformanceLogger.js

@@ -10,9 +10,10 @@
  */
 'use strict';
 
-var BatchedBridge = require('BatchedBridge');
+const BatchedBridge = require('BatchedBridge');
+const fbjsPerformanceNow = require('fbjs/lib/performanceNow');
 
-var performanceNow = require('fbjs/lib/performanceNow');
+const performanceNow = global.nativePerformanceNow || fbjsPerformanceNow;
 
 var timespans = {};
 var extras = {};