[translate] Add translate ranker model loader.

components/translate/core/browser/translate_ranker_impl.h

Index: components/translate/core/browser/translate_ranker_impl.h
diff --git a/components/translate/core/browser/translate_ranker_impl.h b/components/translate/core/browser/translate_ranker_impl.h
new file mode 100644
index 0000000000000000000000000000000000000000..7781705ed36f4b93d6d01d086b0dcb0eb4495f17
--- /dev/null
+++ b/components/translate/core/browser/translate_ranker_impl.h
@@ -0,0 +1,131 @@
+// 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_TRANSLATE_CORE_BROWSER_TRANSLATE_RANKER_IMPL_H_
+#define COMPONENTS_TRANSLATE_CORE_BROWSER_TRANSLATE_RANKER_IMPL_H_
+
+#include <memory>
+#include <string>
+
+#include "base/feature_list.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequence_checker.h"
+#include "base/sequenced_task_runner.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "components/translate/core/browser/ranker_model_loader.h"
+#include "components/translate/core/browser/translate_ranker.h"
+
+namespace chrome_intelligence {
+class RankerModel;
+}  // namespace chrome_intelligence
+
+namespace metrics {
+class TranslateEventProto;
+}  // namespace metrics
+
+namespace translate {
+
+class TranslatePrefs;
+
+// Features used to enable ranker query, enforcement and logging. Note that
+// enabling enforcement implies (forces) enabling queries.
+extern const base::Feature kTranslateRankerQuery;
+extern const base::Feature kTranslateRankerEnforcement;
+extern const base::Feature kTranslateRankerLogging;
+
+struct TranslateRankerFeatures {
+  TranslateRankerFeatures();
+
+  TranslateRankerFeatures(int accepted,
+                          int denied,
+                          int ignored,
+                          const std::string& src,
+                          const std::string& dst,
+                          const std::string& cntry,
+                          const std::string& locale);
+
+  TranslateRankerFeatures(const TranslatePrefs& prefs,
+                          const std::string& src,
+                          const std::string& dst,
+                          const std::string& locale);
+
+  ~TranslateRankerFeatures();
+
+  void WriteTo(std::ostream& stream) const;
+
+  // Input value used to generate the features.
+  int accepted_count;
+  int denied_count;
+  int ignored_count;
+  int total_count;
+
+  // Used for inference.
+  std::string src_lang;
+  std::string dst_lang;
+  std::string country;
+  std::string app_locale;
+  double accepted_ratio;
+  double denied_ratio;
+  double ignored_ratio;
+};
+
+// If enabled, downloads a translate ranker model and uses it to determine
+// whether the user should be given a translation prompt or not.
+class TranslateRankerImpl : public TranslateRanker {
+ public:
+  TranslateRankerImpl(const base::FilePath& model_path, const GURL& model_url);
+  ~TranslateRankerImpl() override;
+
+  // Get the file path of the translate ranker model, by default with a fixed
+  // name within |data_dir|.
+  static base::FilePath GetModelPath(const base::FilePath& data_dir);
+
+  // Get the URL from which the download the translate ranker model, by default
+  // from Finch.
+  static GURL GetModelURL();
+
+  // TranslateRanker...
+  bool IsLoggingEnabled() override;
+  bool IsQueryEnabled() override;
+  bool IsEnforcementEnabled() override;
+  int GetModelVersion() const override;
+  bool ShouldOfferTranslation(const TranslatePrefs& translate_prefs,
+                              const std::string& src_lang,
+                              const std::string& dst_lang) override;
+  void AddTranslateEvent(
+      const metrics::TranslateEventProto& translate_event) override;
+  void FlushTranslateEvents(
+      std::vector<metrics::TranslateEventProto>* events) override;
+
+  void OnModelAvailable(
+      std::unique_ptr<chrome_intelligence::RankerModel> model);
+
+  // Calculate the score given to |features| by the |model|.
+  double CalculateScore(const TranslateRankerFeatures& features);
+
+ private:
+  // Used to sanity check the threading of this ranker.
+  base::SequenceChecker sequence_checker_;
+
+  // A helper to load the translate ranker model from disk cache or a URL.
+  std::unique_ptr<RankerModelLoader> model_loader_;
+
+  // The translation ranker model.
+  std::unique_ptr<chrome_intelligence::RankerModel> model_;
+
+  // Saved cache of translate event protos.
+  std::vector<metrics::TranslateEventProto> event_cache_;
+
+  base::WeakPtrFactory<TranslateRankerImpl> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(TranslateRankerImpl);
+};
+
+}  // namespace translate
+
+std::ostream& operator<<(std::ostream& stream,
+                         const translate::TranslateRankerFeatures& features);
+
+#endif  // COMPONENTS_TRANSLATE_CORE_BROWSER_TRANSLATE_RANKER_IMPL_H_