Use a joinable background thread instead of worker pool in gin

gin/public/v8_platform.h

Index: gin/public/v8_platform.h
diff --git a/gin/public/v8_platform.h b/gin/public/v8_platform.h
index a4fc28a9bc32cf394af4027cddfc116a85219fd1..d1ed077f5c277e5dceba2f61c2a7bd1b01e2e8b3 100644
--- a/gin/public/v8_platform.h
+++ b/gin/public/v8_platform.h
@@ -8,9 +8,14 @@
 #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.
@@ -30,6 +35,7 @@ class GIN_EXPORT V8Platform : public NON_EXPORTED_BASE(v8::Platform) {
 
   V8Platform();
   ~V8Platform() override;
+  scoped_ptr<base::Thread> background_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(V8Platform);
 };