Using STL to implement functionality in input_method_util.cc

chrome/browser/spellchecker/spellcheck_service.cc

 // Copyright (c) 2012 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 "chrome/browser/spellchecker/spellcheck_service.h"
 
+#include <algorithm>
 #include <set>
 
 #include "base/logging.h"
 #include "base/strings/string_split.h"
 #include "base/supports_user_data.h"
 #include "base/synchronization/waitable_event.h"
 #include "build/build_config.h"
 #include "chrome/browser/spellchecker/feedback_sender.h"
 #include "chrome/browser/spellchecker/spellcheck_factory.h"
 #include "chrome/browser/spellchecker/spellcheck_host_metrics.h"
@@ skipping 329 matching lines @@
   std::transform(
       accept_languages.begin(), accept_languages.end(),
       accept_languages.begin(),
       &chrome::spellcheck_common::GetCorrespondingSpellCheckLanguage);
 
   StringListPrefMember dictionaries_pref;
   dictionaries_pref.Init(prefs::kSpellCheckDictionaries, prefs);
   std::vector<std::string> dictionaries = dictionaries_pref.GetValue();
   std::vector<std::string> filtered_dictionaries;
 
-  for (const auto& dictionary : dictionaries) {
-    if (std::find(accept_languages.begin(), accept_languages.end(),
-                  dictionary) != accept_languages.end()) {
-      filtered_dictionaries.push_back(dictionary);
-    }
-  }
+  std::sort(dictionaries.begin(), dictionaries.end());

[groby-ooo-7-16, 2016/04/04 22:30:40]

Before modifying things, please check the history _why_ it's different from what
you think is the better pattern.

In this case, https://codereview.chromium.org/1673783003 - we cannot change the
order of dictionaries because that affects a preference the user has expressed.

[chakshu, 2016/04/11 06:54:37]

Thank you for the review. 
Using unordered_set will improve the performance so I think it is the better
pattern from what has been done till now.
Now I have also taken care that the order of dictionaries does not change. 

+  std::sort(accept_languages.begin(), accept_languages.end());
+  std::set_intersection(dictionaries.begin(), dictionaries.end(),
+                        accept_languages.begin(), accept_languages.end(),
+                        std::back_inserter(filtered_dictionaries));
 
   dictionaries_pref.SetValue(filtered_dictionaries);
 }
 
 void SpellcheckService::UpdateFeedbackSenderState() {
   std::string feedback_language;
   if (!hunspell_dictionaries_.empty())
     feedback_language = hunspell_dictionaries_.front()->GetLanguage();
   std::string language_code;
   std::string country_code;
   chrome::spellcheck_common::GetISOLanguageCountryCodeFromLocale(
       feedback_language, &language_code, &country_code);
   feedback_sender_->OnLanguageCountryChange(language_code, country_code);
   if (SpellingServiceClient::IsAvailable(
           context_, SpellingServiceClient::SPELLCHECK)) {
     feedback_sender_->StartFeedbackCollection();
   } else {
     feedback_sender_->StopFeedbackCollection();
   }
 }