Unify ClassElement and TypedefElement.

lib/compiler/implementation/warnings.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.
 
 class MessageKind {
   final String template;
   const MessageKind(this.template);
 
   static final GENERIC = const MessageKind('#{1}');
 
@@ skipping 104 matching lines @@
   static final EXISTING_LABEL = const MessageKind(
       'original declaration of duplicate label #{1}');
   static final DUPLICATE_LABEL = const MessageKind(
       'duplicate declaration of label #{1}');
   static final UNUSED_LABEL = const MessageKind(
       'unused label #{1}');
   static final INVALID_CONTINUE = const MessageKind(
       'target of continue is not a loop or switch case');
   static final TYPE_VARIABLE_AS_CONSTRUCTOR = const MessageKind(
       'cannot use type variable as constructor');
+  static final DUPLICATE_TYPE_VARIABLE_NAME = const MessageKind(
+      'type variable #{1} already declared');
   static final INVALID_BREAK = const MessageKind(
       'target of break is not a statement');
   static final INVALID_USE_OF_SUPER = const MessageKind(
       'super not allowed here');
   static final INVALID_CASE_DEFAULT = const MessageKind(
       'default only allowed on last case of a switch');
   static final INVALID_CASE_EXPRESSION = const MessageKind(
       'case expression is not a compile-time constant int or string.');
   static final INVALID_CASE_EXPRESSION_TYPE = const MessageKind(
       "case expressions don't all have the same type "
@@ skipping 166 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, List<Type> arguments)
     : super(kind, arguments);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, List<Type> arguments)
     : super(kind, arguments);
 }