Check in codegen test expectations.

test/codegen/expect/language/main_test_20_multi.js

Index: test/codegen/expect/language/main_test_20_multi.js
diff --git a/test/codegen/expect/language/main_test_20_multi.js b/test/codegen/expect/language/main_test_20_multi.js
new file mode 100644
index 0000000000000000000000000000000000000000..631309a845b2b74a5a02207300a73eccd64bffbb
--- /dev/null
+++ b/test/codegen/expect/language/main_test_20_multi.js
@@ -0,0 +1,16 @@
+dart_library.library('language/main_test_20_multi', null, /* Imports */[
+  'dart_sdk'
+], function load__main_test_20_multi(exports, dart_sdk) {
+  'use strict';
+  const core = dart_sdk.core;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const main_test_20_multi = Object.create(null);
+  let __Todynamic = () => (__Todynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [], [dart.dynamic])))();
+  main_test_20_multi.main = function(a) {
+    if (a === void 0) a = null;
+  };
+  dart.fn(main_test_20_multi.main, __Todynamic());
+  // Exports:
+  exports.main_test_20_multi = main_test_20_multi;
+});