[platform] Implement a worker pool

src/libplatform/default-platform.h

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-#ifndef V8_DEFAULT_PLATFORM_H_
-#define V8_DEFAULT_PLATFORM_H_
+#ifndef V8_LIBPLATFORM_DEFAULT_PLATFORM_H_
+#define V8_LIBPLATFORM_DEFAULT_PLATFORM_H_
 
-#include "v8.h"
+#include <vector>
+
+#include "../../include/v8-platform.h"
+// TODO(jochen): We should have our own version of globals.h.
+#include "../globals.h"
+#include "../platform/mutex.h"
+#include "task-queue.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);
+
   // 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 = 4;
+
+  Mutex lock_;
+  bool initialized_;
+  std::vector<WorkerThread*> thread_pool_;
+  TaskQueue queue_;
+
   DISALLOW_COPY_AND_ASSIGN(DefaultPlatform);
 };
 
 
 } }  // namespace v8::internal
 
 
-#endif  // V8_DEFAULT_PLATFORM_H_
+#endif  // V8_LIBPLATFORM_DEFAULT_PLATFORM_H_