fixes #27385, implement virtual fields in DDC

tests/language_strong/field_test.dart

Index: tests/language_strong/field_test.dart
diff --git a/tests/language_strong/field_test.dart b/tests/language_strong/field_test.dart
index ca417404fd2bc424dd3795acc36476af1d38446a..0a34813961a67b60bfa7c35741446178c63e0cc5 100644
--- a/tests/language_strong/field_test.dart
+++ b/tests/language_strong/field_test.dart
@@ -4,11 +4,12 @@
 // Dart test program for testing setting/getting of instance fields.
 
 import "package:expect/expect.dart";
+import "package:meta/meta.dart" show virtual;
 
 class First {
   First() {}
-  var a;
-  var b;
+  @virtual var a;
+  @virtual var b;
 
   addFields() {
     return a + b;