[SyncFS] Create SyncWorkerInterface

chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc

 // 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.
 
 #include <algorithm>
 #include <stack>
 
 #include "base/file_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
@@ skipping 565 matching lines @@
   }
 
   FakeDriveServiceHelper* fake_drive_service_helper() {
     return fake_drive_service_helper_.get();
   }
 
  private:
   // MetadataDatabase is normally used on the worker thread.
   // Use this only when there is no task running on the worker.
   MetadataDatabase* metadata_database() {
-    return remote_sync_service_->sync_worker_
-        ->context_->metadata_database_.get();
+    SyncWorker* worker = static_cast<SyncWorker*>(
+        remote_sync_service_->sync_worker_.get());
+    return worker->context_->metadata_database_.get();
   }
 
   content::TestBrowserThreadBundle thread_bundle_;
 
   base::ScopedTempDir base_dir_;
   scoped_ptr<leveldb::Env> in_memory_env_;
   TestingProfile profile_;
 
   scoped_ptr<SyncEngine> remote_sync_service_;
   scoped_ptr<LocalFileSyncService> local_sync_service_;
@@ skipping 1091 matching lines @@
 
   EXPECT_EQ(1u, CountApp());
   EXPECT_EQ(1u, CountLocalFile(app_id));
 
   EXPECT_EQ(2u, CountMetadata());
   EXPECT_EQ(2u, CountTracker());
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system