Make RequestCache.clear_request_cache a classmethod

common/djangoapps/request_cache/middleware.py

@@ -18,7 +18,11 @@ class RequestCache(object):
         """
         return _request_cache_threadlocal.request
 
-    def clear_request_cache(self):
+    @classmethod
+    def clear_request_cache(cls):
+        """
+        Empty the request cache.
+        """
         _request_cache_threadlocal.data = {}
         _request_cache_threadlocal.request = None