Add support for metadata annotation syntax (issue 4056)

compiler/java/com/google/dart/compiler/parser/Token.java

 // Copyright (c) 2012, 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.
 
 package com.google.dart.compiler.parser;
 
 import java.util.HashMap;
 import java.util.Map;
 
 /**
  * Dart tokens and associated data.
  *
  * Note: Token ordinals matter for some accessors, so don't change the order of these without
  * knowing what you're doing.
  */
 public enum Token {
   /* End-of-stream. */
   EOS(null, 0),
 
   /* Punctuators. */
+  AT("@", 0),
   LPAREN("(", 0),
   RPAREN(")", 0),
   LBRACK("[", 0),
   RBRACK("]", 0),
   LBRACE("{", 0),
   RBRACE("}", 0),
   COLON(":", 0),
   SEMICOLON(";", 0),
   PERIOD(".", 0),
   CASCADE("..", 2),
@@ skipping 221 matching lines @@
 
   @Override
   public String toString() {
     String result = getSyntax();
     if (result == null) {
       return name();
     }
     return result;
   }
 }