Check const map literal keys and switch case exprs using type of constant.

tests/language/const_map3_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 A {
-  const factory A() = B;
+  static const b = const B();
 }
 
 class B implements A {
   const B();
 
   operator ==(o) => true;  /// 00: compile-time error
 }
 
 confuse(x) {

[Brian Wilkerson, 2014/05/03 15:03:34]

I don't think the method 'confuse' adds anything to this test, and should
probably be removed.

[Paul Berry, 2014/05/03 17:14:56]

Done.

   if (new DateTime.now() == 42) return confuse(2);
   return x;
 }
 
 main() {
   // It is a compile-time error if the key type overrides operator ==.
-  var m = const { const A(): 42 };
+  var m = const { A.b: 42 };
   Expect.equals(42, m[confuse(const B())]);
 
-  m = const { "foo": 99, const A(): 499 };
+  m = const { "foo": 99, A.b: 499 };
   Expect.equals(499, m[confuse(const B())]);
 }