chromeos: Destruct DriveResourceMetadata on the blocking pool

chrome/browser/chromeos/drive/drive_system_service.h

Index: chrome/browser/chromeos/drive/drive_system_service.h
diff --git a/chrome/browser/chromeos/drive/drive_system_service.h b/chrome/browser/chromeos/drive/drive_system_service.h
index 6e39149e021449e83dbcc4ce6d73b9805b73f3b2..a01b8a005d3b55e974499bfcbfdd500e6726ffe8 100644
--- a/chrome/browser/chromeos/drive/drive_system_service.h
+++ b/chrome/browser/chromeos/drive/drive_system_service.h
@@ -13,6 +13,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "chrome/browser/chromeos/drive/drive_file_error.h"
+#include "chrome/browser/chromeos/drive/drive_file_system_util.h"
 #include "chrome/browser/profiles/profile_keyed_service.h"
 #include "chrome/browser/profiles/profile_keyed_service_factory.h"
 #include "sync/notifier/invalidation_handler.h"
@@ -93,12 +94,6 @@ class DriveSystemService : public ProfileKeyedService,
       const syncer::ObjectIdInvalidationMap& invalidation_map) OVERRIDE;
 
  private:
-  // Used to destroy DriveCache with scoped_ptr.
-  struct DriveCacheDeleter {
-   public:
-    void operator()(DriveCache* cache) const;
-  };
-
   // Returns true if Drive is enabled.
   // Must be called on UI thread.
   bool IsDriveEnabled();
@@ -132,7 +127,7 @@ class DriveSystemService : public ProfileKeyedService,
 
   scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
   scoped_ptr<EventLogger> event_logger_;
-  scoped_ptr<DriveCache, DriveCacheDeleter> cache_;
+  scoped_ptr<DriveCache, util::DestroyHelper> cache_;
   scoped_ptr<google_apis::DriveServiceInterface> drive_service_;
   scoped_ptr<google_apis::DriveUploader> uploader_;
   scoped_ptr<DriveWebAppsRegistry> webapps_registry_;