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

tests/lib/mirrors/hierarchy_invariants_test.dart

Index: tests/lib/mirrors/hierarchy_invariants_test.dart
diff --git a/tests/lib/mirrors/hierarchy_invariants_test.dart b/tests/lib/mirrors/hierarchy_invariants_test.dart
index e35a076c0de5ada1fe38bc774c343dbe15f96fcd..e2b73cafa4e8eb7e5b384957570c76f5c78784e7 100644
--- a/tests/lib/mirrors/hierarchy_invariants_test.dart
+++ b/tests/lib/mirrors/hierarchy_invariants_test.dart
@@ -24,7 +24,9 @@ checkClass(classMirror) {
   }
   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);
   }