js/libs/ember-1.5.1.js
function(callback, self) {
    var keys = this.keys,
        values = this.values;

    keys.forEach(function(key) {
      var guid = guidFor(key);
      callback.call(self, key, values[guid]);
    });
  }
function(callback, self) {
    var keys = this.keys,
        values = this.values;

    keys.forEach(function(key) {
      var guid = guidFor(key);
      callback.call(self, key, values[guid]);
    });
  }
Iterate over all the keys and values. Calls the function once
for each key, passing in the key and value, in that order.

The keys are guaranteed to be iterated over in insertion order.

@method forEach
@param {Function} callback
@param {*} self if passed, the `this` value inside the
callback. By default, `this` is the map.