Switch libraries to using new tags.

sdk/lib/core/errors.dart

Index: sdk/lib/core/errors.dart
diff --git a/sdk/lib/core/errors.dart b/sdk/lib/core/errors.dart
index c18e174e0190334025f5a67b5a23fd1127245d58..5fbd2d99df880cd324ea1d50c0d3452f8fac8f1a 100644
--- a/sdk/lib/core/errors.dart
+++ b/sdk/lib/core/errors.dart
@@ -2,6 +2,8 @@
 // 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 dart.core;
+
 class Error {
   const Error();
 
@@ -75,7 +77,7 @@ class ArgumentError implements Error {
 }
 
 /**
- * Exception thrown because of an index outside of the valid range.
+ * Error thrown because of an index outside of the valid range.
  *
  */
 class RangeError extends ArgumentError {