Move platform abstraction to base library

src/v8threads.h

 // Copyright 2012 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_V8THREADS_H_
 #define V8_V8THREADS_H_
 
 namespace v8 {
 namespace internal {
 
@@ skipping 78 matching lines @@
   ThreadState* GetFreeThreadState();
 
  private:
   ThreadManager();
   ~ThreadManager();
 
   void DeleteThreadStateList(ThreadState* anchor);
 
   void EagerlyArchiveThread();
 
-  Mutex mutex_;
+  base::Mutex mutex_;
   ThreadId mutex_owner_;
   ThreadId lazily_archived_thread_;
   ThreadState* lazily_archived_thread_state_;
 
   // In the following two lists there is always at least one object on the list.
   // The first object is a flying anchor that is only there to simplify linking
   // and unlinking.
   // Head of linked list of free states.
   ThreadState* free_anchor_;
   // Head of linked list of states in use.
   ThreadState* in_use_anchor_;
 
   Isolate* isolate_;
 
   friend class Isolate;
   friend class ThreadState;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8THREADS_H_