Start supporting default classes.

dart/frog/leg/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 93 matching lines @@
       'unused label #{1}');
   static final INVALID_CONTINUE = const MessageKind(
       'target of continue is not a loop or switch case');
 
   static final NOT_A_COMPILE_TIME_CONSTANT = const MessageKind(
       '#{1} cannot be used as compile-time constant');
 
   static final NO_SUCH_LIBRARY_MEMBER = const MessageKind(
       '#{1} has no member named #{2}');
 
+  static final CANNOT_INSTANTIATE_INTERFACE = const MessageKind(
+      "cannot instantiate interface '#{1}'");
+
   toString() => template;
 }
 
 class Message {
   final kind;
   final List arguments;
   String message;
 
   Message(this.kind, this.arguments);
 
@@ skipping 38 matching lines @@
   String toString() => message.toString();
 }
 
 class CompileTimeConstantError {
   final Message message;
   CompileTimeConstantError.message(this.message);
   CompileTimeConstantError(MessageKind kind, List<Type> arguments)
     : message = new Message(kind, arguments);
   String toString() => message.toString();
 }