Fix a corner case of constant evaluation cycle detection.

tests/language/const_redirect_skips_supertype_test.dart

Index: tests/language/const_redirect_skips_supertype_test.dart
diff --git a/tests/language/const_redirect_skips_supertype_test.dart b/tests/language/const_redirect_skips_supertype_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c84aa6227445eaf2a511049eb082c92e0fe1759b
--- /dev/null
+++ b/tests/language/const_redirect_skips_supertype_test.dart
@@ -0,0 +1,21 @@
+// Copyright (c) 2016, 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.
+
+// Since C redirects to C.named, it doesn't implicitly refer to B's
+// unnamed constructor.  Therefore there is no cycle.
+
+class B {
+  final x;
+  const B() : x = y;
+  const B.named() : x = null;
+}
+class C extends B {
+  const C() : this.named();
+  const C.named() : super.named();
+}
+const y = const C();
+
+main() {
+  print(y);
+}