Implement constant maps.

tests/language/src/CompileTimeConstantCTest.dart

Index: tests/language/src/CompileTimeConstantCTest.dart
diff --git a/tests/language/src/CompileTimeConstantCTest.dart b/tests/language/src/CompileTimeConstantCTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..452b11c68f85e5928f47f638875bfc9c771118f5
--- /dev/null
+++ b/tests/language/src/CompileTimeConstantCTest.dart
@@ -0,0 +1,17 @@
+// 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.
+
+final m1 = const {
+  499: 400 + 99  /// 01: compile-time error
+};
+final m2 = const {
+  "foo" + "bar": 42  /// 02: compile-time error
+};
+
+use(x) => x;
+
+main() {
+  use(m1);
+  use(m2);
+}