Check in codegen test expectations.

test/codegen/expect/language/issue21079_test.js

+dart_library.library('language/issue21079_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__issue21079_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const mirrors = dart_sdk.mirrors;
+  const isolate = dart_sdk.isolate;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const issue21079_test = Object.create(null);
+  let VoidTovoid = () => (VoidTovoid = dart.constFn(dart.definiteFunctionType(dart.void, [])))();
+  issue21079_test.main = function() {
+    expect$.Expect.isTrue(dart.equals(mirrors.reflectClass(dart.wrapType(issue21079_test.MyException)).superclass.reflectedType, dart.wrapType(isolate.IsolateSpawnException)));
+    expect$.Expect.isTrue(dart.equals(mirrors.reflectClass(dart.wrapType(isolate.IsolateSpawnException)).reflectedType, dart.wrapType(isolate.IsolateSpawnException)));
+  };
+  dart.fn(issue21079_test.main, VoidTovoid());
+  issue21079_test.MyException = class MyException extends isolate.IsolateSpawnException {
+    new() {
+      super.new("Test");
+    }
+  };
+  dart.setSignature(issue21079_test.MyException, {
+    constructors: () => ({new: dart.definiteFunctionType(issue21079_test.MyException, [])})
+  });
+  // Exports:
+  exports.issue21079_test = issue21079_test;
+});