Compute frontend/backend specific constants.

tests/language/const_switch_test.dart

+  // Copyright (c) 2014, 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.
+
+import 'package:expect/expect.dart';
+
+class C {
+  final field;
+  const C(this.field);
+}
+
+const c1 = const C(0.0);
+const c2 = const C(0);
+const c3 = const C(0.5 + 0.5);
+const c4 = const C(1);
+
+main() {
+  Expect.equals('0.0', test(c1)); /// 01: ok
+  Expect.equals('0', test(c2));   /// 02: ok
+  Expect.equals('1.0', test(c3)); /// 03: ok
+  Expect.equals('1', test(c4));   /// 04: ok
+}
+
+String test(C c) {
+  switch (c) {
+    case const C(0.0): return '0.0';
+    case const C(0): return '0';
+    case const C(1.0): return '1.0';
+    case const C(1): return '1';
+  }
+  return null;
+}