[mac] Send the system spellchecker language to the renderer.

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 "base/logging.h"
 #include "base/prefs/pref_member.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_split.h"
@@ skipping 63 matching lines @@
   }
 
   // If a user goes back to single language spellchecking make sure there is
   // only one language in the dictionaries preference.
   if (!chrome::spellcheck_common::IsMultilingualSpellcheckEnabled() &&
       dictionaries_pref.GetValue().size() > 1) {
     dictionaries_pref.SetValue(
         std::vector<std::string>(1, first_of_dictionaries));
   }
 
+#if defined(USE_BROWSER_SPELLCHECKER)
+  if (dictionaries_pref.GetValue().empty()) {

[groby-ooo-7-16, 2016/01/19 23:54:14]

Do we really want to mess with prefs here? What happens in the cross-platform
sync case?

[please use gerrit instead, 2016/01/20 02:25:59]

Yes, because the spelling service client is using this preference to determine
whether to be enabled. Also, the client sends this language together with the
spellcheck request.

An alternative is to #ifdef both spelling service client and
SpellCheckMsg_Init() here. I think changing one place is better than multiple.

In fact, since a Mac user has no way of modifying this preference in Chrome, it
should be set to platform spellchecker's language unconditionally.
This preference is not synced, as you can see from its initialization here:

https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/spe...

  user_prefs->RegisterListPref(prefs::kSpellCheckDictionaries,
                               new base::ListValue);

Absence of user_prefs::PrefRegistrySyncable::SYNCABLE_PREF flag indicates that
it's not syncable.

+    std::string language = spellcheck_platform::GetSpellCheckerLanguage();
+    if (!language.empty())
+      dictionaries_pref.SetValue(std::vector<std::string>(1, language));
+  }
+#endif
+
   std::string language_code;
   std::string country_code;
   chrome::spellcheck_common::GetISOLanguageCountryCodeFromLocale(
       first_of_dictionaries,
       &language_code,
       &country_code);
   feedback_sender_.reset(new spellcheck::FeedbackSender(
       context->GetRequestContext(), language_code, country_code));
 
   pref_change_registrar_.Add(
@@ skipping 241 matching lines @@
 }
 
 void SpellcheckService::UpdateFeedbackSenderState() {
   if (SpellingServiceClient::IsAvailable(
           context_, SpellingServiceClient::SPELLCHECK)) {
     feedback_sender_->StartFeedbackCollection();
   } else {
     feedback_sender_->StopFeedbackCollection();
   }
 }