[LanguageModel] Return top languages only with a reasonable sample set

components/translate/core/browser/language_model.h

 // 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_LANGUAGE_MODEL_H_
 #define COMPONENTS_TRANSLATE_CORE_BROWSER_LANGUAGE_MODEL_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 12 matching lines @@
 // languages with insignificant frequency are removed, eventually.
 class LanguageModel : public KeyedService {
  public:
   struct LanguageInfo {
     // The ISO 639 language code.
     std::string language_code;
 
     // The current estimated frequency of the language share, a number between 0
     // and 1 (can be understood as the probability that the next page the user
     // opens is in this language). Frequencies over all LanguageInfos from
-    // GetTopLanguages() sum to 1.
+    // GetTopLanguages() sum to 1 (unless there are no top languages, yet).
     float frequency;
 
     bool operator==(const LanguageInfo& m) const {
       return language_code == m.language_code;
     }
   };
 
   explicit LanguageModel(PrefService* pref_service);
   ~LanguageModel() override;
 
   // Registers profile prefs for the model.
   static void RegisterProfilePrefs(PrefRegistrySimple* registry);
 
   // Returns a list of the languages currently tracked by the model, sorted by
-  // frequency in decreasing order.
+  // frequency in decreasing order. The list is empty, if the model has not
+  // enough data points.
   std::vector<LanguageInfo> GetTopLanguages() const;
 
   // Returns the estimated frequency for the given language or 0 if the language
   // is not among the top languages kept in the model.
   float GetLanguageFrequency(const std::string& language_code) const;
 
   // Informs the model that a page with the given language has been visited.
   void OnPageVisited(const std::string& language_code);
 
  private:
   PrefService* pref_service_;
 
   DISALLOW_COPY_AND_ASSIGN(LanguageModel);
 };
 
 }  // namespace translate
 
 #endif  // COMPONENTS_TRANSLATE_CORE_BROWSER_LANGUAGE_MODEL_H_