code: function collectionStream(collection) {
    if (!hasHandler(collection, 'onStream')) {
      collection.handler('onStream');
    }
  
    return function(filterFn) {
      var stream = utils.through.obj();
      stream.setMaxListeners(0);
  
      var views = this.views;
      var write = writeStream(stream);
  
      setImmediate(function() {
        write(views, filterFn);
        stream.end();
      });
  
      return outStream(stream, collection);
    };
  }
docs: Push a view collection into a vinyl stream.
  
  ```js
  app.posts.toStream(function(file) {
  return file.path !== 'index.hbs';
  })
  ```
  
  @name collection.toStream
  @param {Function} Optionally pass a filter function to use for filtering views.
  @return {Stream}
  @api public