Don't sync kEnableContinuousSpellcheck to mobile platforms.

chrome/browser/spellchecker/spellcheck_factory.cc

Index: chrome/browser/spellchecker/spellcheck_factory.cc
diff --git a/chrome/browser/spellchecker/spellcheck_factory.cc b/chrome/browser/spellchecker/spellcheck_factory.cc
index 3fd085b9fc1b74024ff5c5a34768edf3832272e7..deabf96a0a17273af651190116ef25b8cd19c7b5 100644
--- a/chrome/browser/spellchecker/spellcheck_factory.cc
+++ b/chrome/browser/spellchecker/spellcheck_factory.cc
@@ -76,10 +76,13 @@ void SpellcheckServiceFactory::RegisterProfilePrefs(
       prefs::kSpellCheckDictionary,
       l10n_util::GetStringUTF8(IDS_SPELLCHECK_DICTIONARY));
   user_prefs->RegisterBooleanPref(prefs::kSpellCheckUseSpellingService, false);
-  user_prefs->RegisterBooleanPref(
-      prefs::kEnableContinuousSpellcheck,
-      true,
-      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+#if defined(OS_IOS) || defined(OS_ANDROID)
+  uint32_t flags = PrefRegistry::NO_REGISTRATION_FLAGS;
+#else
+  uint32_t flags = user_prefs::PrefRegistrySyncable::SYNCABLE_PREF;
+#endif
+  user_prefs->RegisterBooleanPref(prefs::kEnableContinuousSpellcheck, true,
+                                  flags);
 }
 
 content::BrowserContext* SpellcheckServiceFactory::GetBrowserContextToUse(