Revert the changes from PR 5152

The changes in 5152 appear to have introduced a
 performance problem on stage, so we're going to
 revert them for now.

cms/djangoapps/contentstore/views/item.py

@@ -644,6 +644,9 @@ def _get_module_info(xblock, rewrite_static_links=True):
             course_id=xblock.location.course_key
         )
 
+    # Pre-cache has changes for the entire course because we'll need it for the ancestor info
+    modulestore().has_changes(modulestore().get_course(xblock.location.course_key, depth=None))
+
     # Note that children aren't being returned until we have a use case.
     return create_xblock_info(xblock, data=data, metadata=own_metadata(xblock), include_ancestor_info=True)
 

cms/djangoapps/contentstore/views/tests/test_item.py

@@ -100,9 +100,9 @@ class GetItemTest(ItemTest):
         return html, resources
 
     @ddt.data(
-        (1, 14, 16, 30, 30),
-        (2, 15, 17, 39, 32),
-        (3, 16, 18, 52, 34),
+        (1, 21, 23, 35, 37),
+        (2, 22, 24, 38, 39),
+        (3, 23, 25, 41, 41),
     )
     @ddt.unpack
     def test_get_query_count(self, branching_factor, chapter_queries, section_queries, unit_queries, problem_queries):

common/lib/xmodule/xmodule/modulestore/mongo/draft.py

@@ -597,6 +597,7 @@ class DraftModuleStore(MongoModuleStore):
             bulk_record.dirty = True
             self.collection.remove({'_id': {'$in': to_be_deleted}}, safe=self.collection.safe)
 
+    @MongoModuleStore.memoize_request_cache
     def has_changes(self, xblock):
         """
         Check if the subtree rooted at xblock has any drafts and thus may possibly have changes