Encode the name for associated items on a trait. Fixes #18048.

src/librustc/metadata/encoder.rs

@@ -1398,6 +1398,8 @@ fn encode_info_for_item(ecx: &EncodeContext,
                         ty::StaticExplicitSelfCategory;
                 }
                 ty::TypeTraitItem(associated_type) => {
+                    encode_name(rbml_w, associated_type.name);
+
                     let elem = ast_map::PathName(associated_type.name);
                     encode_path(rbml_w,
                                 path.clone().chain(Some(elem).into_iter()));