use symbol literals instead of const ctor in packages

pkg/polymer/lib/deserialize.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.
 
 library polymer.deserialize;
 
 import 'dart:convert' show JSON;
 import 'dart:mirrors' show reflect, TypeMirror;
 
 final _typeHandlers = () {
   // TODO(jmesserly): switch to map and symbol literal form when supported.
   var m = new Map();
-  m[const Symbol('dart.core.String')] = (x, _) => x;
-  m[const Symbol('dart.core.Null')] = (x, _) => x;
-  m[const Symbol('dart.core.DateTime')] = (x, _) {
+  m[#dart.core.String] = (x, _) => x;
+  m[#dart.core.Null] = (x, _) => x;
+  m[#dart.core.DateTime] = (x, _) {
     // TODO(jmesserly): shouldn't need to try-catch here
     // See: https://code.google.com/p/dart/issues/detail?id=1878
     try {
       return DateTime.parse(x);
     } catch (e) {
       return new DateTime.now();
     }
   };
-  m[const Symbol('dart.core.bool')] = (x, _) => x != 'false';
-  m[const Symbol('dart.core.int')] =
+  m[#dart.core.bool] = (x, _) => x != 'false';
+  m[#dart.core.int] =
       (x, def) => int.parse(x, onError: (_) => def);
-  m[const Symbol('dart.core.double')] =
+  m[#dart.core.double] =
       (x, def) => double.parse(x, (_) => def);
   return m;
 }();
 
 /**
  * Convert representation of [value] based on type of [defaultValue].
  */
 Object deserializeValue(String value, Object defaultValue, TypeMirror type) {
   var handler = _typeHandlers[type.qualifiedName];
   if (handler != null) return handler(value, defaultValue);
 
   try {
     // If the string is an object, we can parse is with the JSON library.
     // include convenience replace for single-quotes. If the author omits
     // quotes altogether, parse will fail.
     return JSON.decode(value.replaceAll("'", '"'));
 
     // TODO(jmesserly): deserialized JSON is not assignable to most objects in
     // Dart. We should attempt to convert it appropriately.
   } catch(e) {
     // The object isn't valid JSON, return the raw value
     return value;
   }
 }