[SyncFS] Make task invocation in SyncTaskRunner async

chrome/browser/sync_file_system/drive_backend/sync_engine_initializer_unittest.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/sync_engine_initializer.h"
 
 #include "base/bind.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/run_loop.h"
 #include "chrome/browser/drive/drive_api_util.h"
@@ skipping 43 matching lines @@
     sync_context_.reset(new SyncEngineContext(
         fake_drive_service.Pass(),
         scoped_ptr<drive::DriveUploaderInterface>(),
         NULL,
         base::MessageLoopProxy::current(),
         base::MessageLoopProxy::current(),
         base::MessageLoopProxy::current()));
 
     sync_task_manager_.reset(new SyncTaskManager(
         base::WeakPtr<SyncTaskManager::Client>(),
-        1 /* maximum_parallel_task */));
+        1 /* maximum_parallel_task */,
+        base::MessageLoopProxy::current()));
     sync_task_manager_->Initialize(SYNC_STATUS_OK);
   }
 
   virtual void TearDown() OVERRIDE {
     sync_task_manager_.reset();
     metadata_database_.reset();
     sync_context_.reset();
     base::RunLoop().RunUntilIdle();
   }
 
@@ skipping 275 matching lines @@
 
   EXPECT_EQ(0u, CountTrackersForFile(sync_root->file_id()));
   EXPECT_FALSE(HasNoParent(sync_root->file_id()));
 
   EXPECT_EQ(1u, CountFileMetadata());
   EXPECT_EQ(1u, CountFileTracker());
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system