Adding an IO Data and keyed service to previews/

chrome/browser/previews/previews_service.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 CHROME_BROWSER_PREVIEWS_PREVIEWS_SERVICE_H_
+#define CHROME_BROWSER_PREVIEWS_PREVIEWS_SERVICE_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+namespace previews {
+class PreviewsUIService;
+}
+
+// Keyed service that owns a previews::PreviewsUIService.

[Lei Zhang, 2016/09/08 19:06:23]

Can you mention "PreviewsService lives on the UI thread" ?

[RyanSturm, 2016/09/08 20:19:09]

Done.

+class PreviewsService : public KeyedService {
+ public:
+  PreviewsService();
+  ~PreviewsService() override;
+
+  // The UI-thread portion of previews/ inter-thread communication.

[Lei Zhang, 2016/09/08 19:06:23]

This comment doesn't make as much sense.

[RyanSturm, 2016/09/08 20:19:09]

Done.

+  void set_previews_ui_service(
+      std::unique_ptr<previews::PreviewsUIService> previews_ui_service);
+  previews::PreviewsUIService* previews_ui_service() {
+    return previews_ui_service_.get();
+  }
+
+ private:
+  // The UI thread portion of previews/ inter-thread communication.
+  std::unique_ptr<previews::PreviewsUIService> previews_ui_service_;
+
+  DISALLOW_COPY_AND_ASSIGN(PreviewsService);
+};
+
+#endif  // CHROME_BROWSER_PREVIEWS_PREVIEWS_SERVICE_H_