Always split collections and argument lists with trailing commas.

tool/node_format_service.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.
 
 import 'dart:math' as math;
 
 import 'package:js/js.dart';
 
 import 'package:dart_style/dart_style.dart';
 
 @JS()
 @anonymous
 class FormatResult {
   external factory FormatResult({String code, String error});
   external String get code;
   external String get error;
 }
 
 @JS('exports.formatCode')
 external set formatCode(Function formatter);
 
 void main() {
   formatCode = allowInterop((String source) {
     var formatter = new DartFormatter();
 
     var exception;
     try {
-      return new FormatResult(
-          code: new DartFormatter().format(source));
+      return new FormatResult(code: new DartFormatter().format(source));
     } on FormatterException catch (err) {
       // Couldn't parse it as a compilation unit.
       exception = err;
     }
 
     // Maybe it's a statement.
     try {
-      return new FormatResult(
-          code: formatter.formatStatement(source));
+      return new FormatResult(code: formatter.formatStatement(source));
     } on FormatterException catch (err) {
       // There is an error when parsing it both as a compilation unit and a
       // statement, so we aren't sure which one the user intended. As a
       // heuristic, we'll choose that whichever one we managed to parse more of
       // before hitting an error is probably the right one.
       if (_firstOffset(exception) < _firstOffset(err)) {
         exception = err;
       }
     }
 
     // If we get here, it couldn't be parsed at all.
     return new FormatResult(code: source, error: "$exception");
   });
 }
 
 /// Returns the offset of the error nearest the beginning of the file out of
 /// all the errors in [exception].
 int _firstOffset(FormatterException exception) =>
     exception.errors.map((error) => error.offset).reduce(math.min);