Split out libplatform into a separate libary

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);
+
+
+}  // namespace platform
+}  // namespace v8
+
+#endif  // V8_LIBPLATFORM_LIBPLATFORM_H_