Swapping iterator's _next_item() for _item_to_value().

This is so that the owned items iterator management could
be done on the base class and the child classes just
need to worry about converting the JSON values to whatever
type is required.

Author: dhermes

packages/google-cloud-resource-manager/google/cloud/resource_manager/client.py

@@ -173,13 +173,15 @@ class _ProjectPage(Page):
 
     ITEMS_KEY = 'projects'
 
-    def _next_item(self):
-        """Get the next project in the page.
+    def _item_to_value(self, resource):
+        """Convert a JSON project to the native object.
+
+        :type resource: dict
+        :param resource: An resource to be converted to a project.
 
         :rtype: :class:`.Project`
         :returns: The next project in the page.
         """
-        resource = six.next(self._item_iter)
         return Project.from_api_repr(resource, client=self._parent.client)