reset common window methods in .reset?

[lancejpollard]

should we add this here?

var setTimeout = window.setTimeout;
var setInterval = window.setInterval;
var onerror = undefined;
var onload = undefined;

exports.reset = function(){
  for (var i = 0, key; key = this.globals[i]; i++) window[key] = undefined;
  window.setTimeout = setTimeout;
  window.setInterval = setInterval;
  window.onerror = onerror;
  window.onload = onload;
};

if not here, where should we put this? didn't want to put it into analytics.js-integration-tester because sometimes you want to wait until multiple tests have run (at least for now). doesn't seem ideal to have to define this for each integration though, since we could just removing the .global property?

/cc @ianstormtaylor @yields