Add a new magic element type for annotating types that have Javascript array behavior.

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 141 matching lines @@
 
   static final CANNOT_INSTANTIATE_TYPEDEF = const MessageKind(
       "cannot instantiate typedef '#{1}'");
 
   static final NO_DEFAULT_CLASS = const MessageKind(
       "no default class on enclosing interface '#{1}'");
 
   static final CYCLIC_TYPE_VARIABLE = const MessageKind(
       "cyclic reference to type variable #{1}");
   static final TYPE_NAME_EXPECTED = const MessageKind(
-      "class or interface name exptected");
+      "class or interface name expected");
 
   static final CANNOT_EXTEND = const MessageKind(
       "#{1} cannot be extended");
 
   static final CANNOT_IMPLEMENT = const MessageKind(
       "#{1} cannot be implemented");
 
   static final ILLEGAL_SUPER_SEND = const MessageKind(
       "#{1} cannot be called on super");
 
@@ skipping 93 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);
 }