Use ExternalFileSystemBackend in the DriveURLRequestJob.

chrome/browser/chromeos/drive/drive_protocol_handler.h

Index: chrome/browser/chromeos/drive/drive_protocol_handler.h
diff --git a/chrome/browser/chromeos/drive/drive_protocol_handler.h b/chrome/browser/chromeos/drive/drive_protocol_handler.h
index 9c1c796eb7db85fb309db3d3af41c0b7064dcc46..7657e74276d2c906db060960575d27c019c17ca8 100644
--- a/chrome/browser/chromeos/drive/drive_protocol_handler.h
+++ b/chrome/browser/chromeos/drive/drive_protocol_handler.h
@@ -6,7 +6,6 @@
 #define CHROME_BROWSER_CHROMEOS_DRIVE_DRIVE_PROTOCOL_HANDLER_H_
 
 #include "base/basictypes.h"
-#include "base/memory/ref_counted.h"
 #include "net/url_request/url_request_job_factory.h"
 
 namespace base {
@@ -29,9 +28,6 @@ class DriveProtocolHandler : public net::URLRequestJobFactory::ProtocolHandler {
   // The profile for processing Drive accesses. Should not be NULL.
   void* profile_id_;
 
-  // The task runner for operations to communicate with a locally cached file.
-  scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
-
   DISALLOW_COPY_AND_ASSIGN(DriveProtocolHandler);
 };