Allow all different string-literals in map literals.

lib/compiler/implementation/compile_time_constants.dart

 // 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.
 
 class Constant implements Hashable {
   const Constant();
 
   bool isNull() => false;
   bool isBool() => false;
   bool isTrue() => false;
@@ skipping 721 matching lines @@
 
   Constant visitLiteralMap(LiteralMap node) {
     if (!node.isConst()) error(node);
     List<StringConstant> keys = <StringConstant>[];
     Map<StringConstant, Constant> map = new Map<StringConstant, Constant>();
     for (Link<Node> link = node.entries.nodes;
          !link.isEmpty();
          link = link.tail) {
       LiteralMapEntry entry = link.head;
       Constant key = evaluate(entry.key);
-      if (!key.isString() || entry.key.asLiteralString() === null) {
+      if (!key.isString() || entry.key.asStringNode() === null) {
         MessageKind kind = MessageKind.KEY_NOT_A_STRING_LITERAL;
         compiler.reportError(entry.key, new ResolutionError(kind, const []));
       }
       StringConstant keyConstant = key;
       if (!map.containsKey(key)) keys.add(key);
       map[key] = evaluate(entry.value);
     }
     List<Constant> values = <Constant>[];
     Constant protoValue = null;
     for (StringConstant key in keys) {
@@ skipping 372 matching lines @@
       Constant fieldValue = fieldValues[field];
       if (fieldValue === null) {
         // Use the default value.
         fieldValue = compiler.compileVariable(field);
       }
       jsNewArguments.add(fieldValue);          
     });
     return jsNewArguments;
   }
 }