bpo-12414: Update code_sizeof() to take in account co_extra memory. (#1168)

diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index ebc7066..46bc45d 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -451,11 +451,15 @@
 static PyObject *
 code_sizeof(PyCodeObject *co, void *unused)
 {
-    Py_ssize_t res;
+    Py_ssize_t res = _PyObject_SIZE(Py_TYPE(co));
+    _PyCodeObjectExtra *co_extra = (_PyCodeObjectExtra*) co->co_extra;
 
-    res = _PyObject_SIZE(Py_TYPE(co));
     if (co->co_cell2arg != NULL && co->co_cellvars != NULL)
         res += PyTuple_GET_SIZE(co->co_cellvars) * sizeof(Py_ssize_t);
+
+    if (co_extra != NULL)
+        res += co_extra->ce_size * sizeof(co_extra->ce_extras[0]);
+
     return PyLong_FromSsize_t(res);
 }