Mark Library 'mode' field non-editable.

The only supported mode is currently 'random', so it doesn't make sense
to expose the 'mode' in the edit form.

common/lib/xmodule/xmodule/library_content_module.py

@@ -322,6 +322,15 @@ class LibraryContentDescriptor(LibraryContentFields, MakoModuleDescriptor, XmlDe
     js = {'coffee': [resource_string(__name__, 'js/src/vertical/edit.coffee')]}
     js_module_name = "VerticalDescriptor"
 
+    @property
+    def non_editable_metadata_fields(self):
+        non_editable_fields = super(LibraryContentDescriptor, self).non_editable_metadata_fields
+        # The only supported mode is currently 'random'.
+        # Add the mode field to non_editable_metadata_fields so that it doesn't
+        # render in the edit form.
+        non_editable_fields.append(LibraryContentFields.mode)
+        return non_editable_fields
+
     @XBlock.handler
     def refresh_children(self, request=None, suffix=None):  # pylint: disable=unused-argument
         """

common/lib/xmodule/xmodule/tests/test_library_content.py

@@ -5,7 +5,7 @@ Basic unit tests for LibraryContentModule
 Higher-level tests are in `cms/djangoapps/contentstore/tests/test_libraries.py`.
 """
 import ddt
-from xmodule.library_content_module import LibraryVersionReference, ANY_CAPA_TYPE_VALUE
+from xmodule.library_content_module import LibraryVersionReference, ANY_CAPA_TYPE_VALUE, LibraryContentDescriptor
 from xmodule.modulestore.tests.factories import LibraryFactory, CourseFactory, ItemFactory
 from xmodule.modulestore.tests.utils import MixedSplitTestCase
 from xmodule.tests import get_test_system
@@ -242,3 +242,12 @@ class TestLibraries(MixedSplitTestCase):
         self.lc_block.capa_type = ANY_CAPA_TYPE_VALUE
         self.lc_block.refresh_children()
         self.assertEqual(len(self.lc_block.children), len(self.lib_blocks) + 4)
+
+    def test_non_editable_settings(self):
+        """
+        Test the settings that are marked as "non-editable".
+        """
+        non_editable_metadata_fields = self.lc_block.non_editable_metadata_fields
+        self.assertIn(LibraryContentDescriptor.mode, non_editable_metadata_fields)
+        self.assertNotIn(LibraryContentDescriptor.display_name, non_editable_metadata_fields)
+