Add dart_messages package.

pkg/compiler/lib/src/diagnostics/messages.dart

 // Copyright (c) 2011, 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 dart2js.messages;
 
+import 'package:dart_messages/shared_messages.dart' as shared_messages;
+
 import '../tokens/token.dart' show ErrorToken, Token;
 
 import 'invariant.dart' show invariant;
 import 'spannable.dart' show CURRENT_ELEMENT_SPANNABLE;
 
 import 'dart2js_messages.dart' as dart2js_messages;
-import 'shared_messages.dart' as shared_messages;
 
 /// Keys for the [MessageTemplate]s.
 enum MessageKind {
   ABSTRACT_CLASS_INSTANTIATION,
   ABSTRACT_GETTER,
   ABSTRACT_METHOD,
   ABSTRACT_SETTER,
   ACCESSED_IN_CLOSURE,
   ACCESSED_IN_CLOSURE_HERE,
   ADDITIONAL_ARGUMENT,
@@ skipping 963 matching lines @@
   static String convertToString(value) {
     if (value is ErrorToken) {
       // Shouldn't happen.
       return value.assertionMessage;
     } else if (value is Token) {
       value = value.value;
     }
     return '$value';
   }
 }