Allow built-in identifiers for labels.

dart/lib/compiler/implementation/scanner/parser.dart

 // 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.
 
 /**
  * An event generating parser of Dart programs. This parser expects
  * all tokens in a linked list (aka a token stream).
  *
  * The class [Scanner] is used to generate a token stream. See the
  * file scanner.dart.
@@ skipping 756 matching lines @@
     } else if (value === 'try') {
       return parseTryStatement(token);
     } else if (value === 'switch') {
       return parseSwitchStatement(token);
     } else if (value === 'break') {
       return parseBreakStatement(token);
     } else if (value === 'continue') {
       return parseContinueStatement(token);
     } else if (value === ';') {
       return parseEmptyStatement(token);
+    } else if (isIdentifier(token)) {
+      return parseExpressionStatementOrDeclaration(token);
     } else {
       return parseExpressionStatement(token);
     }
   }
 
   Token parseReturnStatement(Token token) {
     Token begin = token;
     listener.beginReturnStatement(begin);
     assert('return' === token.stringValue);
     token = token.next;
@@ skipping 883 matching lines @@
     }
     listener.handleContinueStatement(hasTarget, continueKeyword, token);
     return expectSemicolon(token);
   }
 
   Token parseEmptyStatement(Token token) {
     listener.handleEmptyStatement(token);
     return expectSemicolon(token);
   }
 }