Check in codegen test expectations.

test/codegen/expect/language/null_to_string2_test.js

+dart_library.library('language/null_to_string2_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__null_to_string2_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const null_to_string2_test = Object.create(null);
+  let VoidToA = () => (VoidToA = dart.constFn(dart.definiteFunctionType(null_to_string2_test.A, [])))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  null_to_string2_test.A = class A extends core.Object {};
+  null_to_string2_test.foo = function() {
+    return null;
+  };
+  dart.fn(null_to_string2_test.foo, VoidToA());
+  null_to_string2_test.main = function() {
+    let nullObj = null_to_string2_test.foo();
+    let x = dart.toString(nullObj);
+    expect$.Expect.isTrue(typeof x == 'string');
+    let y = dart.bind(nullObj, 'toString', dart.toString);
+    expect$.Expect.isNotNull(y);
+  };
+  dart.fn(null_to_string2_test.main, VoidTodynamic());
+  // Exports:
+  exports.null_to_string2_test = null_to_string2_test;
+});