Allow Symbols in switch and maps

tests/language/symbol_literal_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 symbol literals.
 
 library symbol_literal_test;
 
 import 'package:expect/expect.dart';
 
 foo(a, b) => Expect.isTrue(identical(a, b));
 
 var check = foo; // Indirection used to avoid inlining.
 
+testSwitch(Symbol s) {
+  switch(s) {
+    case #abc: return 1;
+    case const Symbol("def"): return 2;
+    default: return 0;
+  }
+}
+
 main() {
   check(const Symbol("a"), #a);
   check(const Symbol("a"), #
                             a);
   check(const Symbol("ab"), #ab);
   check(const Symbol("ab"), #
                              ab);
   check(const Symbol("a.b"), #a.b);
   check(const Symbol("a.b"), #
                               a
                                .
                                 b);
   check(const Symbol("=="), #==);
   check(const Symbol("=="), # ==);
   check(const Symbol("a.toString"), #a.toString);
 
+  Expect.equals(1, testSwitch(#abc));
+
+  const m = const <Symbol, int>{#A:0, #B:1};
+  Expect.equals(1, m[#B]);
+
   // Tries to call the symbol literal #a.toString
   Expect.throws(() => #a.toString(), (e) => e is NoSuchMethodError); /// 01: static type warning
 }