Add countable interface to classes with count() method

Author: Ben Batschelet

lib/internal/Magento/Framework/DB/Tree/NodeSet.php

@@ -9,7 +9,7 @@
  * TODO implements iterators
  *
  */
-class NodeSet implements \Iterator
+class NodeSet implements \Iterator, \Countable
 {
     /**
      * @var Node[]

lib/internal/Magento/Framework/Data/Form/Element/Collection.php

@@ -13,7 +13,7 @@
  *
  * @author      Magento Core Team <core@magentocommerce.com>
  */
-class Collection implements \ArrayAccess, \IteratorAggregate
+class Collection implements \ArrayAccess, \IteratorAggregate, \Countable
 {
     /**
      * Elements storage

lib/internal/Magento/Framework/Data/Tree/Node/Collection.php

@@ -17,7 +17,7 @@
 /**
  * @api
  */
-class Collection implements \ArrayAccess, \IteratorAggregate
+class Collection implements \ArrayAccess, \IteratorAggregate, \Countable
 {
     /**
      * @var array