Support FutureOr<T> in the VM (fixes #28010).

tests/lib/mirrors/hierarchy_invariants_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.hierarchy_invariants_test;
 
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
 isAnonymousMixinApplication(classMirror) {
   return MirrorSystem.getName(classMirror.simpleName).contains(' with ');
 }
 
 checkClass(classMirror) {
   Expect.isTrue(classMirror.simpleName is Symbol);
   Expect.notEquals(null, classMirror.owner);
   Expect.isTrue(classMirror.owner is LibraryMirror);
   if (!isAnonymousMixinApplication(classMirror)) {
     Expect.equals(classMirror.originalDeclaration,
                   classMirror.owner.declarations[classMirror.simpleName]);
   } else {
     Expect.isNull(classMirror.owner.declarations[classMirror.simpleName]);
   }
   Expect.isTrue(classMirror.superinterfaces is List);
   if (classMirror.superclass == null) {
-    Expect.equals(reflectClass(Object), classMirror);

[rmacnak, 2017/01/17 17:58:07]

I don't see why your change would affect this property. The superclass of
FutureOr is still Object.

[regis, 2017/01/17 18:10:20]

Somehow, the mirrors implementation is using VM types instead of actual classes.
This results in the classMirror for FutureOr to use the type FutureOr that has
been mapped to dynamic. The resulting classMirror is very similar to the
classMirror for dynamic, i.e it has no superclass, but its name still refers to
'FutureOr'.

[rmacnak, 2017/01/17 18:20:59]

I see. LGTM w/ bug filed against this test change.

+    Expect.isTrue(classMirror == reflectClass(Object) ||
+                  // Type FutureOr is mapped to dynamic in the VM.
+                  classMirror.toString() == "ClassMirror on 'FutureOr'");
   } else {
     checkClass(classMirror.superclass);
   }
 }
 
 checkLibrary(libraryMirror) {
   libraryMirror.declarations.values
       .where((d) => d is ClassMirror)
       .forEach(checkClass);
 }
 
 main() {
   currentMirrorSystem().libraries.values.forEach(checkLibrary);
 }