Add command-line parameter enabling assert messages.

pkg/compiler/lib/src/scanner/partial_parser.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 scanner;
 
 class PartialParser extends Parser {
-  PartialParser(Listener listener) : super(listener);
+  PartialParser(Listener listener, {bool allowAssertMessage: false})
+      : super(listener, allowAssertMessage: allowAssertMessage);
 
   Token parseClassBody(Token token) => skipClassBody(token);
 
   Token fullParseClassBody(Token token) => super.parseClassBody(token);
 
   Token parseExpression(Token token) => skipExpression(token);
 
   Token parseArgumentsOpt(Token token) {
     // This method is overridden for two reasons:
     // 1. Avoid generating events for arguments.
@@ skipping 138 matching lines @@
         return token;
       }
       return listener.unexpected(token);
     }
     BeginGroupToken beginGroupToken = token;
     Token endToken = beginGroupToken.endGroup;
     listener.endFormalParameters(0, token, endToken);
     return endToken.next;
   }
 }