[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlay_service/overlay_service_factory.h

+// Copyright 2017 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 IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_OVERLAY_SERVICE_FACTORY_H_
+#define IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_OVERLAY_SERVICE_FACTORY_H_
+
+#include "base/macros.h"
+#include "components/keyed_service/ios/browser_state_keyed_service_factory.h"
+
+namespace base {
+template <typename T>
+struct DefaultSingletonTraits;
+}
+
+namespace ios {
+class ChromeBrowserState;
+}
+
+class OverlayService;
+
+// OverlayServiceFactory attaches OverlayServices to ChromeBrowserStates.
+class OverlayServiceFactory : public BrowserStateKeyedServiceFactory {
+ public:
+  // Convenience getter that typecasts the value returned to OverlayService.
+  static OverlayService* GetForBrowserState(
+      ios::ChromeBrowserState* browser_state);
+  // Getter for singleton instance.
+  static OverlayServiceFactory* GetInstance();
+
+ private:
+  friend struct base::DefaultSingletonTraits<OverlayServiceFactory>;
+
+  OverlayServiceFactory();
+  ~OverlayServiceFactory() override;
+
+  // BrowserStateKeyedServiceFactory implementation.
+  std::unique_ptr<KeyedService> BuildServiceInstanceFor(
+      web::BrowserState* context) const override;
+
+  DISALLOW_COPY_AND_ASSIGN(OverlayServiceFactory);
+};
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_UI_OVERLAYS_OVERLAY_SERVICE_FACTORY_H_