Constructs a DisplayBag object.
\Drupal\views\ViewExecutable: The view which has this displays attached.
\Drupal\Component\Plugin\PluginManagerInterface $manager: The manager to be used for instantiating plugins.
public function __construct(ViewExecutable $view, PluginManagerInterface $manager) {
$this->view = $view;
$this->manager = $manager;
$this
->initializePlugin('default');
// Store all display IDs to access them easy and fast.
$display = $this->view->storage
->get('display');
$this->instanceIDs = drupal_map_assoc(array_keys($display));
}