Check in codegen test expectations.

test/codegen/expect/corelib/iterable_first_test.js

+dart_library.library('corelib/iterable_first_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__iterable_first_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const _interceptors = dart_sdk._interceptors;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const iterable_first_test = Object.create(null);
+  let JSArrayOfint = () => (JSArrayOfint = dart.constFn(_interceptors.JSArray$(core.int)))();
+  let JSArrayOfString = () => (JSArrayOfString = dart.constFn(_interceptors.JSArray$(core.String)))();
+  let SetOfint = () => (SetOfint = dart.constFn(core.Set$(core.int)))();
+  let VoidToString = () => (VoidToString = dart.constFn(dart.definiteFunctionType(core.String, [])))();
+  let dynamicTobool = () => (dynamicTobool = dart.constFn(dart.definiteFunctionType(core.bool, [dart.dynamic])))();
+  let VoidTovoid = () => (VoidTovoid = dart.constFn(dart.definiteFunctionType(dart.void, [])))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  let const$;
+  iterable_first_test.main = function() {
+    let list1 = JSArrayOfint().of([1, 2, 3]);
+    let list2 = const$ || (const$ = dart.constList([4, 5], core.int));
+    let list3 = JSArrayOfString().of([]);
+    let set1 = SetOfint().new();
+    set1.add(11);
+    set1.add(12);
+    set1.add(13);
+    let set2 = core.Set.new();
+    expect$.Expect.equals(1, list1[dartx.first]);
+    expect$.Expect.equals(4, list2[dartx.first]);
+    expect$.Expect.throws(dart.fn(() => list3[dartx.first], VoidToString()), dart.fn(e => core.StateError.is(e), dynamicTobool()));
+    expect$.Expect.isTrue(set1.contains(set1.first));
+    expect$.Expect.throws(dart.fn(() => set2.first, VoidTovoid()), dart.fn(e => core.StateError.is(e), dynamicTobool()));
+  };
+  dart.fn(iterable_first_test.main, VoidTodynamic());
+  // Exports:
+  exports.iterable_first_test = iterable_first_test;
+});