Support compile time constant conditional expressions

tests/language/compile_time_constant11_test.dart

Index: tests/language/compile_time_constant11_test.dart
===================================================================
--- tests/language/compile_time_constant11_test.dart	(revision 0)
+++ tests/language/compile_time_constant11_test.dart	(revision 0)
@@ -0,0 +1,25 @@
+// Copyright (c) 2012, 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.
+
+// Check that conditional expression can be a compile-time constant.
+
+import "package:expect/expect.dart";
+
+const C1 = true;
+const C2 = false;
+
+const nephew = C1 ? C2 ? "Tick" : "Trick" : "Track";
+
+main() {
+  const a = true ? 5 : 10;
+  const b = C2 ? "Track" : C1 ? "Trick" : "Tick";
+
+  Expect.equals(5, a);
+  Expect.equals("Trick", nephew);
+  Expect.equals(nephew, b);
+  Expect.identical(nephew, b);
+  var s = const Symbol(nephew);
+  var msg = "Donald is $nephew's uncle.";
+  Expect.equals("Donald is Trick's uncle.", msg);
+}