Add LanguageModel, a keyed service that collects language info from CLD.

components/translate/core/browser/language_model.cc

Index: components/translate/core/browser/language_model.cc
diff --git a/components/translate/core/browser/language_model.cc b/components/translate/core/browser/language_model.cc
new file mode 100644
index 0000000000000000000000000000000000000000..60c435a80d8ed83c0f0a24463852737a08678de1
--- /dev/null
+++ b/components/translate/core/browser/language_model.cc
@@ -0,0 +1,127 @@
+// 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/language_model.h"
+
+#include <algorithm>
+#include <map>
+#include <set>
+
+#include "components/prefs/pref_registry_simple.h"
+#include "components/prefs/pref_service.h"
+#include "components/prefs/scoped_user_pref_update.h"
+
+namespace translate {
+
+namespace {
+
+const char kLanguageModelCounters[] = "language_model_counters";
+
+const int kMaxCountersSum = 1000;
+const float kCutoffRatio = 0.005f;
+const float kDiscountFactor = 0.75f;
+
+// Gets the sum of the counter for all languages in the model.
+int GetCountersSum(const base::DictionaryValue& dict) {
+  int sum = 0;
+  int counter_value = 0;
+  for (base::DictionaryValue::Iterator itr(dict); !itr.IsAtEnd();
+       itr.Advance()) {
+    if (itr.value().GetAsInteger(&counter_value))
+      sum += counter_value;
+  }
+  return sum;
+}
+
+// Removes languages with small counter values and discount remaining counters.
+void DiscountAndCleanCounters(base::DictionaryValue* dict) {
+  std::set<std::string> remove_keys;
+
+  int counter_value = 0;
+  for (base::DictionaryValue::Iterator itr(*dict); !itr.IsAtEnd();
+       itr.Advance()) {
+    // Remove languages with invalid or small values.
+    if (!itr.value().GetAsInteger(&counter_value) ||
+        counter_value < (kCutoffRatio * kMaxCountersSum)) {
+      remove_keys.insert(itr.key());
+      continue;
+    }
+
+    // Discount the value.
+    dict->SetInteger(itr.key(), counter_value * kDiscountFactor);
+  }
+
+  for (const std::string& lang_to_remove : remove_keys)
+    dict->Remove(lang_to_remove, nullptr);
+}
+
+// Transforms the counters from prefs into a list of LanguageInfo structs.
+std::vector<LanguageModel::LanguageInfo> GetAllLanguages(
+    const base::DictionaryValue& dict) {
+
+  std::vector<LanguageModel::LanguageInfo> top_languages;
+  int counters_sum = GetCountersSum(dict);
+
+  int counter_value = 0;
+  for (base::DictionaryValue::Iterator itr(dict); !itr.IsAtEnd();
+       itr.Advance()) {
+    if (!itr.value().GetAsInteger(&counter_value))
+      continue;
+    top_languages.push_back(
+        {itr.key(), static_cast<float>(counter_value) / counters_sum});
+  }
+  return top_languages;
+}
+
+}  // namespace
+
+LanguageModel::LanguageModel(PrefService* pref_service)
+    : pref_service_(pref_service) {}
+
+LanguageModel::~LanguageModel() = default;
+
+// static
+void LanguageModel::RegisterProfilePrefs(PrefRegistrySimple* registry) {
+  registry->RegisterDictionaryPref(kLanguageModelCounters);
+}
+
+std::vector<LanguageModel::LanguageInfo> LanguageModel::GetTopLanguages()
+    const {
+  std::vector<LanguageModel::LanguageInfo> top_languages =
+      GetAllLanguages(*pref_service_->GetDictionary(kLanguageModelCounters));
+
+  std::sort(top_languages.begin(), top_languages.end(),
+            [](LanguageModel::LanguageInfo a, LanguageModel::LanguageInfo b) {
+              return a.frequency > b.frequency;
+            });
+
+  return top_languages;
+}
+
+float LanguageModel::GetLanguageFrequency(
+    const std::string& language_code) const {
+  const base::DictionaryValue* dict =
+      pref_service_->GetDictionary(kLanguageModelCounters);
+  int counter_value = 0;
+  // If the key |language_code| does not exist, |counter_value| stays 0.
+  dict->GetInteger(language_code, &counter_value);
+
+  int counters_sum = GetCountersSum(*dict);
+
+  return static_cast<float>(counter_value) / counters_sum;
+}
+
+void LanguageModel::OnPageVisited(const std::string& language_code) {
+  DictionaryPrefUpdate update(pref_service_, kLanguageModelCounters);
+  base::DictionaryValue* dict = update.Get();
+  int counter_value = 0;
+  // If the key |language_code| does not exist, |counter_value| stays 0.
+  dict->GetInteger(language_code, &counter_value);
+  dict->SetInteger(language_code, counter_value + 1);
+
+  if (GetCountersSum(*dict) > kMaxCountersSum)
+    DiscountAndCleanCounters(dict);
+}
+
+}  // namespace translate