code: function makeObserver(handlers) {
    console.assert(handlers && typeof handlers === 'object', "Argument to makeObserver must be hash.");
    var handler = assign(create(observerPrototype), handlers);
    var observer = handler.handle.bind(handler);
    observer.keys = getTypesFromHandlers(handlers);
    return observer;
  }
docs: Make an observer from a hash of handlers for observation types. This observer can be passed to `observeObject`.