Make argument to StringSink.writeln optional.

pkg/scheduled_test/test/metatest.dart

 // Copyright (c) 2013, 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.
 
 /// A test library for testing test libraries? We must go deeper.
 ///
 /// Since unit testing code tends to use a lot of global state, it can be tough
 /// to test. This library manages it by running each test case in a child
 /// isolate, then reporting the results back to the parent isolate.
 library metatest;
@@ skipping 135 matching lines @@
 String _summarizeTests(Map results) {
   var buffer = new StringBuffer();
   for (var t in results["results"]) {
     buffer.writeln("${t['result'].toUpperCase()}: ${t['description']}");
     if (t['message'] != '') buffer.writeln("${_indent(t['message'])}");
     if (t['stackTrace'] != null && t['stackTrace'] != '') {
       buffer.writeln("${_indent(t['stackTrace'])}");
     }
   }
 
-  buffer.writeln("");
+  buffer.writeln();
 
   var success = false;
   if (results['passed'] == 0 && results['failed'] == 0 &&
       results['errors'] == 0 && results['uncaughtError'] == null) {
     buffer.write('No tests found.');
     // This is considered a failure too.
   } else if (results['failed'] == 0 && results['errors'] == 0 &&
       results['uncaughtError'] == null) {
     buffer.write('All ${results['passed']} tests passed.');
     success = true;
@@ skipping 39 matching lines @@
         "message": testCase.message,
         "result": testCase.result,
         "stackTrace": testCase.stackTrace
       }).toList()
     });
   }
 
   void onInit() {}
   void onDone(bool success) {}
 }