Support enums in dart2js.

pkg/compiler/lib/src/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.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 1965 matching lines @@
 
   static const MessageKind HIDDEN_HINTS = const MessageKind(
       "#{hints} hint(s) suppressed in #{uri}.");
 
   static const MessageKind PREAMBLE = const MessageKind(
     "When run on the command-line, the compiled output might"
     " require a preamble file located in:\n"
     "  <sdk>/lib/_internal/compiler/js_lib/preambles.");
 
 
+  static const MessageKind EXPERIMENTAL_ENUMS = const MessageKind(
+      "Experimental language feature 'enums' is not supported.",
+      howToFix: "Use option '--enable-enum' to use enum declarations.",
+      examples: const ["""
+enum Enum { A, B, C }
+main() => print(Enum.A);
+"""]);
+
   static const MessageKind EXPERIMENTAL_ASYNC_AWAIT = const MessageKind(
       "Experimental language feature 'async/await' is not supported.");
 
   static const MessageKind INVALID_STARRED_KEYWORD = const MessageKind(
       "Invalid '#{keyword}' keyword.",
       options: const ['--enable-async'],
       howToFix: "Try removing whitespace between '#{keyword}' and '*'.",
       examples: const [
         "main() async * {}",
         "main() sync * {}",
@@ skipping 238 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';
   }
 }