/**
  * Initializes extension driver
  *
  * @param ObjectManager $objectManager
  * @param string $extensionNamespace
  * @param object $annotationReader
  */
 public function __construct($objectManager, $extensionNamespace, $annotationReader)
 {
     $this->objectManager = $objectManager;
     $this->annotationReader = $annotationReader;
     $this->extensionNamespace = $extensionNamespace;
     $omDriver = $objectManager->getConfiguration()->getMetadataDriverImpl();
     $this->driver = $this->getDriver($omDriver);
 }