Check in codegen test expectations.

test/codegen/expect/lib/html/private_extension_member_test.js

+dart_library.library('lib/html/private_extension_member_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__private_extension_member_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const html = dart_sdk.html;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const private_extension_member_test = Object.create(null);
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  private_extension_member_test.main = function() {
+    expect$.Expect.equals("[object DocumentFragment]", dart.toString(html.BRElement.new()[dartx.createFragment]("Hi")));
+  };
+  dart.fn(private_extension_member_test.main, VoidTodynamic());
+  // Exports:
+  exports.private_extension_member_test = private_extension_member_test;
+});