[translate] Add translate ranker model loader.

components/translate/core/browser/ranker_model.cc

+// 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.
+
+#include "components/translate/core/browser/ranker_model.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/time/time.h"
+#include "components/translate/core/browser/proto/ranker_model.pb.h"
+
+namespace chrome_intelligence {
+
+RankerModel::RankerModel() : proto_(base::MakeUnique<RankerModelProto>()) {}
+
+RankerModel::~RankerModel() {}
+
+// static
+std::unique_ptr<RankerModel> RankerModel::FromString(const std::string& data) {
+  auto model = base::MakeUnique<RankerModel>();
+  if (!model->mutable_proto()->ParseFromString(data))
+    return nullptr;
+  return model;
+}
+
+bool RankerModel::IsExpired() const {
+  if (!proto().has_metadata())
+    return true;
+
+  const auto& metadata = proto().metadata();
+
+  // If the age of the model cannot be determined, presume it to be expired.
+  if (!metadata.has_last_modified_sec())
+    return true;
+
+  // If the model has no set cache duration, then it never expires.
+  if (!metadata.has_cache_duration_sec() || metadata.cache_duration_sec() == 0)
+    return false;
+
+  // Otherwise, a model is expired if its age exceeds the cache duration.
+  base::Time last_modified =
+      base::Time() + base::TimeDelta::FromSeconds(metadata.last_modified_sec());
+  base::TimeDelta age = base::Time::Now() - last_modified;
+  return age > base::TimeDelta::FromSeconds(metadata.cache_duration_sec());
+}
+
+const std::string& RankerModel::GetSourceURL() const {
+  return proto_->metadata().source();
+}
+
+std::string RankerModel::SerializeAsString() const {
+  return proto_->SerializeAsString();
+}
+
+}  // namespace chrome_intelligence