old_contents: define('polyfill', [], function() {
      // polyfill window.location.origin only available in FF21+
      var loc = window.location;
      if (!loc.origin) {
          loc.origin = loc.protocol + '//' + loc.host;
      }
  });
  
new_contents: define('polyfill', [], function() {
      // Polyfill `window.location.origin` (available in only FF 21+).
      var loc = window.location;
      if (!loc.origin) {
          loc.origin = loc.protocol + '//' + loc.host;
      }
  
      // Polyfill `window.performance.now`
      // (available in only IE 10+, FF 15+, Chrome 20+, PhantomJS 2).
      if (!window.performance) {
          window.performance = {};
      }
      if (!window.performance.now) {
          window.performance.now = function() {
              // Avoid using `Date.now` for IE 8 and lower.
              return +new Date();
          };
      }
  });
  
subject: add `window.performance.now` polyfill (bug 1090572)