[translate] Add translate ranker model loader.

ios/chrome/browser/translate/translate_ranker_factory.h

+// 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.
+
+#ifndef IOS_CHROME_BROWSER_TRANSLATE_TRANSLATE_RANKER_FACTORY_H_
+#define IOS_CHROME_BROWSER_TRANSLATE_TRANSLATE_RANKER_FACTORY_H_
+
+#include <memory>
+
+#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;
+}
+
+namespace translate {
+
+class TranslateRanker;
+
+// TranslateRankerFactory is a way to associate a TranslateRanker instance to
+// a BrowserState.
+class TranslateRankerFactory : public BrowserStateKeyedServiceFactory {
+ public:
+  static translate::TranslateRanker* GetForBrowserState(
+      ios::ChromeBrowserState* browser_state);
+  static TranslateRankerFactory* GetInstance();
+
+ private:
+  friend struct base::DefaultSingletonTraits<TranslateRankerFactory>;
+
+  TranslateRankerFactory();
+  ~TranslateRankerFactory() override;
+
+  // BrowserStateKeyedServiceFactory implementation.
+  std::unique_ptr<KeyedService> BuildServiceInstanceFor(
+      web::BrowserState* context) const override;
+  web::BrowserState* GetBrowserStateToUse(
+      web::BrowserState* context) const override;
+
+  DISALLOW_COPY_AND_ASSIGN(TranslateRankerFactory);
+};
+
+}  // namespace translate
+
+#endif  // IOS_CHROME_BROWSER_TRANSLATE_TRANSLATE_RANKER_FACTORY_H_