Two minor bug fixes: a type error in the parser, and throwing the

dart/frog/leg/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.
 
 class PartialParser extends Parser {
   PartialParser(Listener listener) : super(listener);
 
   Token parseClassBody(Token token) => skipBlock(token);
 
   Token fullParseClassBody(Token token) => super.parseClassBody(token);
@@ skipping 31 matching lines @@
       token = skipBlock(token);
     }
     // There is no "skipped function body event", so we use
     // handleNoFunctionBody instead.
     listener.handleNoFunctionBody(token);
     return token;
   }
 
   Token parseFormalParameters(Token token) => skipFormals(token);
 
-  Token skipFormals(BeginGroupToken token) {
+  Token skipFormals(Token token) {
     listener.beginOptionalFormalParameters(token);
-    expect('(', token);
-    Token endToken = token.endGroup;
+    if (!optional('(', token)) {
+      if (optional(';', token)) {
+        listener.recoverableError("expected '('", token: token);
+        return token;
+      }
+      return listener.unexpected(token);
+    }
+    BeginGroupToken beginGroupToken = token;
+    Token endToken = beginGroupToken.endGroup;
     listener.endFormalParameters(0, token, endToken);
     return endToken.next;
   }
 }