ignore trailing whitespace in polymer transform test

pkg/polymer/test/transform/all_phases_test.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.
 
 library polymer.test.transform.all_phases_test;
 
 import 'package:polymer/src/transform.dart';
 import 'package:unittest/compact_vm_config.dart';
 
 import 'common.dart';
@@ skipping 193 matching lines @@
 String _sampleObservableOutput(String className, String fieldName) => '''
 library ${className}_$fieldName;
 import 'package:observe/observe.dart';
 
 class $className extends ChangeNotifierBase {
   int __\$$fieldName;
   int get $fieldName => __\$$fieldName;
   set $fieldName(int value) {
     __\$$fieldName = notifyPropertyChange(const Symbol('$fieldName'), __\$$fieldName, value);
   }
-  
+
   $className($fieldName) : __\$$fieldName = $fieldName;
 }
 ''';