Remove parallel marking support.

src/marking-thread.h

-// Copyright 2013 the V8 project authors. All rights reserved.
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-
-#ifndef V8_MARKING_THREAD_H_
-#define V8_MARKING_THREAD_H_
-
-#include "atomicops.h"
-#include "flags.h"
-#include "platform.h"
-#include "v8utils.h"
-
-#include "spaces.h"
-
-#include "heap.h"
-
-namespace v8 {
-namespace internal {
-
-class MarkingThread : public Thread {
- public:
-  explicit MarkingThread(Isolate* isolate);
-  ~MarkingThread() {}
-
-  void Run();
-  void Stop();
-  void StartMarking();
-  void WaitForMarkingThread();
-
- private:
-  Isolate* isolate_;
-  Heap* heap_;
-  Semaphore start_marking_semaphore_;
-  Semaphore end_marking_semaphore_;
-  Semaphore stop_semaphore_;
-  volatile AtomicWord stop_thread_;
-  int id_;
-  static Atomic32 id_counter_;
-};
-
-} }  // namespace v8::internal
-
-#endif  // V8_MARKING_THREAD_H_