dart2dart fix synthesized constructor appearing in unparser. Don't output it.

lib/compiler/implementation/dart_backend/backend.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.
 
 class BailoutException {
   final String reason;
 
   const BailoutException(this.reason);
 }
 
@@ skipping 39 matching lines @@
    * Outputs given class element with given inner elements to a string buffer.
    */
   void outputClass(ClassElement classElement, List<Element> innerElements,
       StringBuffer sb) {
     // TODO(smok): Very soon properly print out correct class declaration with
     // extends, implements, etc.
     sb.add('class ');
     sb.add(classElement.name.slowToString());
     sb.add('{');
     innerElements.forEach((element) {
+      if (element is SynthesizedConstructorElement) return;
       // TODO(smok): Filter out default constructors here.
       sb.add(element.parseNode(compiler).unparse());
     });
     sb.add('}');
   }
 
   void assembleProgram() {
     resolvedElements.forEach((element, treeElements) {
       unparseValidator.check(element);
     });
@@ skipping 57 matching lines @@
       compiler.assembledCode = '''
 main() {
   final bailout_reason = "${e.reason}";
 }
 ''';
     }
   }
 
   log(String message) => compiler.log('[DartBackend] $message');
 }