Improve parsing of async and generator methods.

pkg/front_end/lib/src/fasta/scanner/token.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.
 
 library fasta.scanner.token;
 
 import 'keyword.dart' show Keyword;
 
 import 'precedence.dart' show BAD_INPUT_INFO, EOF_INFO, PrecedenceInfo;
 
@@ skipping 78 matching lines @@
    * The precedence level for this token.
    */
   int get precedence => info.precedence;
 
   /**
    * True if this token is an identifier. Some keywords allowed as identifiers,
    * see implementation in [KeywordToken].
    */
   bool isIdentifier();
 
+  bool get isPseudo => false;
+
   /**
    * Returns a textual representation of this token to be used for debugging
    * purposes. The resulting string might contain information about the
    * structure of the token, for example 'StringToken(foo)' for the identifier
    * token 'foo'.
    *
    * Use [lexeme] for the text actually parsed by the token.
    */
   String toString();
 
@@ skipping 62 matching lines @@
   KeywordToken(this.keyword, int charOffset) : super(charOffset);
 
   PrecedenceInfo get info => keyword.info;
 
   String get lexeme => keyword.syntax;
 
   String get stringValue => keyword.syntax;
 
   bool isIdentifier() => keyword.isPseudo || keyword.isBuiltIn;
 
+  bool get isPseudo => keyword.isPseudo;
+
   bool get isBuiltInIdentifier {
     // TODO(ahe): Remove special case for "deferred" once dartbug.com/29069 is
     // fixed.
     return keyword.isBuiltIn || identical("deferred", lexeme);
   }
 
   String toString() => "KeywordToken($lexeme)";
 }
 
 /**
@@ skipping 187 matching lines @@
       identical(value, "<=") ||
       identical(value, "<") ||
       identical(value, "&") ||
       identical(value, "^") ||
       identical(value, "|");
 }
 
 bool isTernaryOperator(String value) => identical(value, "[]=");
 
 bool isMinusOperator(String value) => identical(value, "-");