Require case expressions to be compile-time constants

tests/language/switch_int_double_test.dart

 // Copyright (c) 2013, 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.
 
-// Test that double literals with no fractional part is not treated as having
-// static type int.
+// Test reporting a compile-time error if case expressions do not all have
+// the same type.
 
 import "package:expect/expect.dart";
 
 void main() {
   Expect.equals(100, test(1.0));
   Expect.equals(75, test(0.75));
   Expect.equals(null, test(0.5));
 }
 
 int test(num ratio) {
   switch (ratio) {
     case 0.75:
       return 75;
     case 1.0:
       return 100;
     case 2:       /// 01: compile-time error
       return 200; /// 01: continued
     case 'foo':   /// 02: compile-time error
       return 400; /// 02: continued
   }
 }