Metadata API should examine child serializer if passed parent ListSerializer. Closes #2035.

rest_framework/metadata.py

@@ -96,6 +96,10 @@ class SimpleMetadata(BaseMetadata):
         Given an instance of a serializer, return a dictionary of metadata
         about its fields.
         """
+        if hasattr(serializer, 'child'):
+            # If this is a `ListSerializer` then we want to examine the
+            # underlying child serializer instance instead.
+            serializer = serializer.child
         return OrderedDict([
             (field_name, self.get_field_info(field))
             for field_name, field in serializer.fields.items()