Initializing formals can't be optional parameters

tests/language/src/TryCatch3Test.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.
 // Dart test program for testing try/catch statement without any exceptions
 // being thrown.
 
 interface TestException {
   String getMessage();
 }
 
 class MyException implements TestException {
-  const MyException([String this.message_ = ""]);
-  String getMessage() { return message_; }
-  final String message_;
+  const MyException([String message = ""]) : this._message = message;
+  String getMessage() { return _message; }
+  final String _message;
 }
 
 class MyParameterizedException<U, V> implements TestException {
-  const MyParameterizedException([String this.message_ = ""]);
-  String getMessage() { return message_; }
-  final String message_;
+  const MyParameterizedException([String message = ""])
+      : this._message = message;
+  String getMessage() { return _message; }
+  final String _message;
 }
 
 class StackTrace {
   StackTrace() { }
   printStackTrace(TestException ex) {
     print(ex);
   }
 }
 
 class Helper {
@@ skipping 74 matching lines @@
 
 class TryCatchTest {
   static testMain() {
     Expect.equals(900, Helper.test1(1));
   }
 }
 
 main() {
   TryCatchTest.testMain();
 }