Migrate to using core-object.

[rwjblue]

Instead of:

function MixinFileInfo(options) {
  options.type = 'util';

  ClassicFileInfo.apply(this, arguments);
}
MixinFileInfo.prototype = Object.create(ClassicFileInfo.prototype);
MixinFileInfo.prototype.constructor = MixinFileInfo;

MixinFileInfo.prototype.populateDestination = function() {
};

We should be able to do this:

var MixinFileInfo = FileInfo.extend({
  init: function(options) {
    options.type = 'util';
    this._super(options);
  },

  populateDestination: function() { }
});

[trabus]

Starting work on this now. Should hopefully have a PR by the end of the night!