Change the calling conventions for handleUnrecoverableError.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

 // Copyright (c) 2016, 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.body_builder;
 
 import '../parser/parser.dart' show FormalParameterType, optional;
 
 import '../parser/error_kind.dart' show ErrorKind;
 
@@ skipping 2181 matching lines @@
     if (isDartLibrary && kind == ErrorKind.ExpectedFunctionBody) {
       Token recover = skipNativeClause(token);
       if (recover != null) return recover;
     } else if (kind == ErrorKind.UnexpectedToken) {
       String expected = arguments["expected"];
       const List<String> trailing = const <String>[")", "}", ";", ","];
       if (trailing.contains(token.stringValue) && trailing.contains(expected)) {
         arguments.putIfAbsent("actual", () => token.value);
         handleRecoverableError(token, ErrorKind.ExpectedButGot, arguments);
       }
-      return token;
+      return newSyntheticToken(token);
     }
     return super.handleUnrecoverableError(token, kind, arguments);
   }
 
   @override
   Expression buildCompileTimeError(error, [int charOffset = -1]) {
     String message = printUnexpected(uri, charOffset, error);
     Builder constructor = library.loader.getCompileTimeError();
     return new Throw(buildStaticInvocation(constructor.target,
         new Arguments(<Expression>[new StringLiteral(message)]),
@@ skipping 479 matching lines @@
   } else if (node is TypeDeclarationBuilder) {
     return node.name;
   } else if (node is PrefixBuilder) {
     return node.name;
   } else if (node is ThisPropertyAccessor) {
     return node.name.name;
   } else {
     return internalError("Unhandled: ${node.runtimeType}");
   }
 }