Reland "Merge more Kernel infrastructure from kernel_sdk SDK fork."

tests/kernel/unsorted/let_test.dart

Index: tests/kernel/unsorted/let_test.dart
diff --git a/tests/standalone/fields_may_be_reset_test.dart b/tests/kernel/unsorted/let_test.dart
similarity index 74%
copy from tests/standalone/fields_may_be_reset_test.dart
copy to tests/kernel/unsorted/let_test.dart
index 3ab6fc62450cf34b84362d6af3c911dcf8c7327c..249ec491558b4a1d5eb4999498c45f5dbba2b6ab 100644
--- a/tests/standalone/fields_may_be_reset_test.dart
+++ b/tests/kernel/unsorted/let_test.dart
@@ -2,8 +2,9 @@
 // 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.
 
-// VMOptions=--fields_may_be_reset
+import 'expect.dart';
 
 main() {
-  print("Okay");
+  var a = [1];
+  Expect.isTrue((a..add(42))[1] == 42);
 }