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

chrome/browser/spellchecker/spellcheck_service.cc

Index: chrome/browser/spellchecker/spellcheck_service.cc
diff --git a/chrome/browser/spellchecker/spellcheck_service.cc b/chrome/browser/spellchecker/spellcheck_service.cc
index 7943c1d267006292c7d8433270d7299dcb7e34f1..dcc904301e89b028828210c306ca8fc17bbbf9b1 100644
--- a/chrome/browser/spellchecker/spellcheck_service.cc
+++ b/chrome/browser/spellchecker/spellcheck_service.cc
@@ -81,6 +81,14 @@ SpellcheckService::SpellcheckService(content::BrowserContext* context)
         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(