Remove string constants from Types class.

dart/tests/language/prefix_core_test.dart

Index: dart/tests/language/prefix_core_test.dart
diff --git a/dart/tests/language/prefix_core_test.dart b/dart/tests/language/prefix_core_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..a510ebd101b730487658659479d1b7b7d7dff874
--- /dev/null
+++ b/dart/tests/language/prefix_core_test.dart
@@ -0,0 +1,12 @@
+// 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.
+
+// Test that Object can be resolved when importing dart:core with a prefix.
+
+#import('dart:core', prefix:'core');
+
+class Object {
+}
+
+main() => core.print(new Object());