[platform] Implement a worker pool

src/libplatform/worker-thread.h

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-#ifndef V8_HYDROGEN_MINUS_ZERO_H_
-#define V8_HYDROGEN_MINUS_ZERO_H_
+#ifndef V8_LIBPLATFORM_WORKER_THREAD_H_
+#define V8_LIBPLATFORM_WORKER_THREAD_H_
 
-#include "hydrogen.h"
+#include <queue>
+
+// TODO(jochen): We should have our own version of globals.h.
+#include "../globals.h"
+#include "../platform.h"
 
 namespace v8 {
+
 namespace internal {
 
+class TaskQueue;
 
-class HComputeMinusZeroChecksPhase : public HPhase {
+class WorkerThread : public Thread {
  public:
-  explicit HComputeMinusZeroChecksPhase(HGraph* graph)
-      : HPhase("H_Compute minus zero checks", graph),
-        visited_(graph->GetMaximumValueID(), zone()) { }
+  explicit WorkerThread(TaskQueue* queue);
+  virtual ~WorkerThread();
 
-  void Run();
+  // Thread implementation.
+  virtual void Run() V8_OVERRIDE;
 
  private:
-  void PropagateMinusZeroChecks(HValue* value);
+  friend class QuitTask;
 
-  BitVector visited_;
+  TaskQueue* queue_;
 
-  DISALLOW_COPY_AND_ASSIGN(HComputeMinusZeroChecksPhase);
+  DISALLOW_COPY_AND_ASSIGN(WorkerThread);
 };
 
-
 } }  // namespace v8::internal
 
-#endif  // V8_HYDROGEN_MINUS_ZERO_H_
+
+#endif  // V8_LIBPLATFORM_WORKER_THREAD_H_