[translate] Add ranker model proto and loader.

components/translate/core/browser/ranker_model_unittest.cc

+// 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.
+
+#include "components/translate/core/browser/ranker_model.h"
+
+#include <memory>
+
+#include "base/memory/ptr_util.h"
+#include "base/time/time.h"
+#include "components/translate/core/browser/proto/ranker_model.pb.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+using chrome_intelligence::RankerModel;
+
+const char kModelURL[] = "https://some.url.net/model";
+
+int64_t InSeconds(const base::Time& t) {

[droger, 2017/03/22 14:30:07]

Time should be passed by value (here and in other places in this file).
See comment in time.h
https://cs.chromium.org/chromium/src/base/time/time.h?rcl=ec080c375b6006502f1...

[Roger McFarlane (Chromium), 2017/03/22 20:31:43]

Done.

+  return (t - base::Time()).InSeconds();
+}
+
+std::unique_ptr<RankerModel> NewModel(const std::string& model_url,
+                                      const base::Time& last_modified,
+                                      const base::TimeDelta& cache_duration) {
+  auto model = base::MakeUnique<RankerModel>();
+  auto* metadata = model->mutable_proto()->mutable_metadata();
+  if (!model_url.empty())
+    metadata->set_source(model_url);
+  if (!last_modified.is_null()) {
+    auto last_modified_sec = InSeconds(last_modified);
+    metadata->set_last_modified_sec(last_modified_sec);
+  }
+  if (!cache_duration.is_zero())
+    metadata->set_cache_duration_sec(cache_duration.InSeconds());
+
+  auto* translate = model->mutable_proto()->mutable_translate();
+  translate->set_version(1);
+
+  auto* logit = translate->mutable_logistic_regression_model();
+  logit->set_bias(0.1f);
+  logit->set_accept_ratio_weight(0.2f);
+  logit->set_decline_ratio_weight(0.3f);
+  logit->set_ignore_ratio_weight(0.4f);
+  return model;
+}
+
+}  // namespace
+
+TEST(RankerModelTest, Serialization) {
+  auto last_modified = base::Time::Now();
+  auto cache_duration = base::TimeDelta::FromDays(3);
+  auto original_model = NewModel(kModelURL, last_modified, cache_duration);
+  auto original_model_as_string = original_model->SerializeAsString();

[droger, 2017/03/22 14:30:07]

Nit, optional: I think the code would be clearer with fewer uses of auto.
In particular std::string is not much longer to type than auto.

[Roger McFarlane (Chromium), 2017/03/22 20:31:43]

Done.

+  auto serialized_model = RankerModel::FromString(original_model_as_string);
+  auto serialized_model_as_string = serialized_model->SerializeAsString();
+
+  EXPECT_EQ(serialized_model_as_string, original_model_as_string);
+  EXPECT_EQ(serialized_model->GetSourceURL(), kModelURL);
+  EXPECT_EQ(serialized_model->proto().metadata().last_modified_sec(),
+            InSeconds(last_modified));
+  EXPECT_EQ(serialized_model->proto().metadata().cache_duration_sec(),
+            cache_duration.InSeconds());
+}
+
+TEST(RankerModelTest, IsExpired) {
+  const auto today = base::Time::Now();
+  const auto days_15 = base::TimeDelta::FromDays(15);
+  const auto days_30 = base::TimeDelta::FromDays(30);
+  const auto days_60 = base::TimeDelta::FromDays(60);
+
+  EXPECT_FALSE(NewModel(kModelURL, today, days_30)->IsExpired());
+  EXPECT_FALSE(NewModel(kModelURL, today - days_15, days_30)->IsExpired());
+  EXPECT_TRUE(NewModel(kModelURL, today - days_60, days_30)->IsExpired());
+}