monkeypatch tracking origins onto Promise

promiseOriginMonkeypatch.js

var promiseSource = new WeakMap()
(function(){
  const promiseConstructor = Promise.constructor
  Promise.constructor = function(fn){
    console.log("monkeypatch successful")
    promiseConstructor.call(this, fn)
    promiseSource.set(this, new Error().stack)
  }
}())
var sample = new Promise(x => x(42)) // expecting: "monkeypatch successful"