Buildfix for windows after r22180

include/libplatform/libplatform.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_LIBPLATFORM_LIBPLATFORM_H_
 #define V8_LIBPLATFORM_LIBPLATFORM_H_
 
 #include "include/v8-platform.h"
 
 namespace v8 {
 namespace platform {
 
 /**
  * Returns a new instance of the default v8::Platform implementation.
  *
  * The caller will take ownership of the returned pointer. |thread_pool_size|
  * is the number of worker threads to allocate for background jobs. If a value
  * of zero is passed, a suitable default based on the current number of
  * processors online will be chosen.
  */
-v8::Platform* CreateDefaultPlatform(int thread_pool_size);
+v8::Platform* CreateDefaultPlatform(int thread_pool_size = 0);
 
 
 }  // namespace platform
 }  // namespace v8
 
 #endif  // V8_LIBPLATFORM_LIBPLATFORM_H_