Implement cycle-checking and code generation for redirecting constructors.

frog/tests/leg_only/src/CyclicConstructorTest.dart

Index: frog/tests/leg_only/src/CyclicConstructorTest.dart
diff --git a/frog/tests/leg_only/src/CyclicConstructorTest.dart b/frog/tests/leg_only/src/CyclicConstructorTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..41aa0f66084a336fe75bfa55d7530a16c469c949
--- /dev/null
+++ b/frog/tests/leg_only/src/CyclicConstructorTest.dart
@@ -0,0 +1,17 @@
+// Copyright (c) 2011, 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.
+
+class A {
+  A();
+  A.a() : this.b();
+  A.b() : this.a();
+  A.c() : this.b();
+}
+
+main() {
+  new A();
+  new A.a();  /// 01: compile-time error
+  new A.b();  /// 02: compile-time error
+  new A.c();  /// 03: compile-time error
+}