use symbol literals instead of const ctor in packages

pkg/polymer/lib/src/loader.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.
 
 part of polymer;
 
 /** Annotation used to automatically register polymer elements. */
 class CustomTag {
   final String tagName;
   const CustomTag(this.tagName);
@@ skipping 58 matching lines @@
   if (uri.scheme == '' && srcUrl != null) {
     uri = Uri.parse(path.normalize(path.join(path.dirname(srcUrl), uriString)));
   }
   var lib = _libs[uri];
   if (lib == null) {
     print('warning: $uri library not found');
     return;
   }
 
   // Invoke `main`, if present.
-  if (lib.functions[const Symbol('main')] != null) {
-    lib.invoke(const Symbol('main'), const []);
+  if (lib.functions[#main] != null) {
+    lib.invoke(#main, const []);
   }
 
   // Search top-level functions marked with @initMethod
   for (var f in lib.functions.values) {
     _maybeInvoke(lib, f);
   }
 
   for (var c in lib.classes.values) {
     // Search for @CustomTag on classes
     for (var m in c.metadata) {
@@ skipping 30 matching lines @@
     print("warning: methods marked with @initMethod should take no "
         "arguments, ${method.simpleName} expects some.");
     return;
   }
   obj.invoke(method.simpleName, const []);
 }
 
 class _InitMethodAnnotation {
   const _InitMethodAnnotation();
 }