Fix refactoring bug

tests/standalone/src/ProcessTestUtil.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.
 
 String getPlatformOutDir() {
   var os = new Platform().operatingSystem();
   if (os == 'linux') return 'out';
-  if (os == 'macos') 'xcodebuild';
+  if (os == 'macos') return 'xcodebuild';
   return '';  // Windows.
 }
 
 String getProcessTestFileName() {
   var outDir = getPlatformOutDir();
   var names = ['$outDir/Release_ia32/process_test',
                '$outDir/Debug_ia32/process_test'];
 
   for (var name in names) {
     if (new File(name).existsSync()) {
       return name;
     }
   }
   Expect.fail('Could not find the process_test executable.');
 }
 
 String getDartFileName() {
   var outDir = getPlatformOutDir();
   var names = ['$outDir/Release_ia32/dart',
                '$outDir/Debug_ia32/dart'];
 
   for (var name in names) {
     if (new File(name).existsSync()) {
       return name;
     }
   }
   Expect.fail('Could not find the dart executable.');
 }