performance.now()-polyfill.js

// if Navigation Timing is not supported, fallback to Date.naw() called on start (sufficient in many cases)
// Date.now is also polyfilled
(function(p){
  if(!Date.now)
    Date.now = function(){return +new Date};
  
  if (!p.now){
    var start = (p.timing && p.timing.navigationStart) || Date.now();
    p.now = function now(){
      return Date.now() - start;
    };
  }
})( this.performance || ( this.performance = {} ) );