use symbol literals instead of const ctor

R=rnystrom@google.com, sigmund@google.com

Review URL: https://codereview.chromium.org//26734004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/path@28485 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/lib/path.dart b/lib/path.dart
index eb126d5..dafb0c2 100644
--- a/lib/path.dart
+++ b/lib/path.dart
@@ -90,11 +90,9 @@
 /// return the current URL.
 String get current {
   if (_io != null) {
-    return _io.classes[const Symbol('Directory')]
-        .getField(const Symbol('current')).reflectee.path;
+    return _io.classes[#Directory].getField(#current).reflectee.path;
   } else if (_html != null) {
-    return _html.getField(const Symbol('window'))
-        .reflectee.location.href;
+    return _html.getField(#window).reflectee.location.href;
   } else {
     return '.';
   }
@@ -869,8 +867,8 @@
   static Style _getPlatformStyle() {
     if (_io == null) return Style.url;
 
-    if (_io.classes[const Symbol('Platform')]
-        .getField(const Symbol('operatingSystem')).reflectee == 'windows') {
+    if (_io.classes[#Platform].getField(#operatingSystem)
+        .reflectee == 'windows') {
       return Style.windows;
     }