[SyncFS] Calculate MD5 on FILE thread instead of Worker.

chrome/browser/sync_file_system/drive_backend/local_to_remote_syncer.cc

 // Copyright 2013 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.
 
 #include "chrome/browser/sync_file_system/drive_backend/local_to_remote_syncer.h"
 
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
@@ skipping 384 matching lines @@
 void LocalToRemoteSyncer::UploadExistingFile(
     const SyncStatusCallback& callback)  {
   DCHECK(remote_file_tracker_);
   DCHECK(remote_file_tracker_->has_synced_details());
   DCHECK(sync_context_->GetWorkerTaskRunner()->RunsTasksOnCurrentThread());
 
   base::Callback<void(const std::string&)> did_calculate_callback =
       base::Bind(&LocalToRemoteSyncer::DidGetMD5ForUpload,
                  weak_ptr_factory_.GetWeakPtr(), callback);
 
-  sync_context_->GetWorkerTaskRunner()->PostTask(
+  sync_context_->GetFileTaskRunner()->PostTask(
       FROM_HERE,
       CreateComposedFunction(
           base::Bind(&drive::util::GetMd5Digest, local_path_),
           RelayCallbackToTaskRunner(
               sync_context_->GetWorkerTaskRunner(), FROM_HERE,
               did_calculate_callback)));
 }
 
 void LocalToRemoteSyncer::DidGetMD5ForUpload(
     const SyncStatusCallback& callback,
@@ skipping 288 matching lines @@
   set_used_network(true);
   return sync_context_->GetDriveUploader();
 }
 
 MetadataDatabase* LocalToRemoteSyncer::metadata_database() {
   return sync_context_->GetMetadataDatabase();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system