js/libs/ember-1.5.1.js
function(key, value) {
    var keys = this.keys,
        values = this.values,
        guid = guidFor(key);

    keys.add(key);
    values[guid] = value;
    set(this, 'length', keys.list.length);
  }
function(key, value) {
    var keys = this.keys,
        values = this.values,
        guid = guidFor(key);

    keys.add(key);
    values[guid] = value;
    set(this, 'length', keys.list.length);
  }
Adds a value to the map. If a value for the given key has already been
provided, the new value will replace the old value.

@method set
@param {*} key
@param {*} value