Move platform abstraction to base library

src/libplatform/worker-thread.h

 // Copyright 2013 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_WORKER_THREAD_H_
 #define V8_LIBPLATFORM_WORKER_THREAD_H_
 
 #include <queue>
 
 #include "src/base/macros.h"
-#include "src/platform.h"
+#include "src/base/platform/platform.h"
 
 namespace v8 {
 
 namespace internal {
 
 class TaskQueue;
 
-class WorkerThread : public Thread {
+class WorkerThread : public base::Thread {
  public:
   explicit WorkerThread(TaskQueue* queue);
   virtual ~WorkerThread();
 
   // Thread implementation.
   virtual void Run() V8_OVERRIDE;
 
  private:
   friend class QuitTask;
 
   TaskQueue* queue_;
 
   DISALLOW_COPY_AND_ASSIGN(WorkerThread);
 };
 
 } }  // namespace v8::internal
 
 
 #endif  // V8_LIBPLATFORM_WORKER_THREAD_H_