Move platform abstraction to base library

src/libplatform/default-platform.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_DEFAULT_PLATFORM_H_
 #define V8_LIBPLATFORM_DEFAULT_PLATFORM_H_
 
 #include <vector>
 
 #include "include/v8-platform.h"
 #include "src/base/macros.h"
+#include "src/base/platform/mutex.h"
 #include "src/libplatform/task-queue.h"
-#include "src/platform/mutex.h"
 
 namespace v8 {
 namespace internal {
 
 class TaskQueue;
 class Thread;
 class WorkerThread;
 
 class DefaultPlatform : public Platform {
  public:
   DefaultPlatform();
   virtual ~DefaultPlatform();
 
   void SetThreadPoolSize(int thread_pool_size);
 
   void EnsureInitialized();
 
   // v8::Platform implementation.
   virtual void CallOnBackgroundThread(
       Task *task, ExpectedRuntime expected_runtime) V8_OVERRIDE;
   virtual void CallOnForegroundThread(v8::Isolate *isolate,
                                       Task *task) V8_OVERRIDE;
 
  private:
   static const int kMaxThreadPoolSize;
 
-  Mutex lock_;
+  base::Mutex lock_;
   bool initialized_;
   int thread_pool_size_;
   std::vector<WorkerThread*> thread_pool_;
   TaskQueue queue_;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultPlatform);
 };
 
 
 } }  // namespace v8::internal
 
 
 #endif  // V8_LIBPLATFORM_DEFAULT_PLATFORM_H_