Use a joinable background thread instead of worker pool in gin

gin/public/v8_platform.h

 // Copyright 2014 The Chromium 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 GIN_PUBLIC_V8_PLATFORM_H_
 #define GIN_PUBLIC_V8_PLATFORM_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/lazy_instance.h"
+#include "base/memory/scoped_ptr.h"
 #include "gin/gin_export.h"
 #include "v8/include/v8-platform.h"
 
+namespace base {
+class Thread;
+}
+
 namespace gin {
 
 // A v8::Platform implementation to use with gin.
 class GIN_EXPORT V8Platform : public NON_EXPORTED_BASE(v8::Platform) {
  public:
   static V8Platform* Get();
 
   // v8::Platform implementation.
   void CallOnBackgroundThread(
       v8::Task* task,
       v8::Platform::ExpectedRuntime expected_runtime) override;
   void CallOnForegroundThread(v8::Isolate* isolate, v8::Task* task) override;
   double MonotonicallyIncreasingTime() override;
 
  private:
   friend struct base::DefaultLazyInstanceTraits<V8Platform>;
 
   V8Platform();
   ~V8Platform() override;
+  scoped_ptr<base::Thread> background_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(V8Platform);
 };
 
 }  // namespace gin
 
 #endif  // GIN_PUBLIC_V8_PLATFORM_H_