Check in codegen test expectations.

test/codegen/expect/js/js.js

Index: test/codegen/expect/js/js.js
diff --git a/test/codegen/expect/js/js.js b/test/codegen/expect/js/js.js
new file mode 100644
index 0000000000000000000000000000000000000000..2fed93910cf4e993b68aad6fd3ef59600bb54239
--- /dev/null
+++ b/test/codegen/expect/js/js.js
@@ -0,0 +1,31 @@
+dart_library.library('js', null, /* Imports */[
+  'dart_sdk'
+], function load__js(exports, dart_sdk) {
+  'use strict';
+  const core = dart_sdk.core;
+  const js = dart_sdk.js;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const js$ = Object.create(null);
+  js$.JS = class JS extends core.Object {
+    new(name) {
+      if (name === void 0) name = null;
+      this.name = name;
+    }
+  };
+  dart.setSignature(js$.JS, {
+    constructors: () => ({new: dart.definiteFunctionType(js$.JS, [], [core.String])})
+  });
+  js$._Anonymous = class _Anonymous extends core.Object {
+    new() {
+    }
+  };
+  dart.setSignature(js$._Anonymous, {
+    constructors: () => ({new: dart.definiteFunctionType(js$._Anonymous, [])})
+  });
+  js$.anonymous = dart.const(new js$._Anonymous());
+  js$.allowInteropCaptureThis = js.allowInteropCaptureThis;
+  js$.allowInterop = js.allowInterop;
+  // Exports:
+  exports.js = js$;
+});