Changed previews component to be a layered component.

components/previews/previews_io_data.h

-// Copyright 2016 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.
-
-#ifndef COMPONENTS_PREVIEWS_PREVIEWS_IO_DATA_H_
-#define COMPONENTS_PREVIEWS_PREVIEWS_IO_DATA_H_
-
-#include <string>
-
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/weak_ptr.h"
-#include "base/single_thread_task_runner.h"
-#include "base/threading/thread_checker.h"
-
-namespace previews {
-class PreviewsUIService;
-
-// A class to manage the IO portion of inter-thread communication between
-// previews/ objects. Created on the UI thread, but used only on the IO thread
-// after initialization.
-class PreviewsIOData {
- public:
-  PreviewsIOData(
-      const scoped_refptr<base::SingleThreadTaskRunner>& ui_task_runner,
-      const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner);
-  virtual ~PreviewsIOData();
-
-  // Stores |previews_ui_service| as |previews_ui_service_| and posts a task to
-  // InitializeOnIOThread on the IO thread.
-  void Initialize(base::WeakPtr<PreviewsUIService> previews_ui_service);
-
- protected:
-  // Posts a task to SetIOData for |previews_ui_service_| on the UI thread with
-  // a weak pointer to |this|. Virtualized for testing.
-  virtual void InitializeOnIOThread();
-
- private:
-  // The UI thread portion of the inter-thread communication for previews.
-  base::WeakPtr<PreviewsUIService> previews_ui_service_;
-
-  // The UI and IO thread task runners. |ui_task_runner_| is used to post
-  // tasks to |previews_ui_service_|, and |io_task_runner_| is used to post from
-  // Initialize to InitializeOnIOThread as well as verify that execution is
-  // happening on the IO thread.
-  scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
-  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
-
-  base::WeakPtrFactory<PreviewsIOData> weak_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(PreviewsIOData);
-};
-
-}  // namespace previews
-
-#endif  // COMPONENTS_PREVIEWS_PREVIEWS_IO_DATA_H_