Make the ARC opt-in preference not synced.

chrome/browser/chromeos/arc/arc_auth_service.cc

Index: chrome/browser/chromeos/arc/arc_auth_service.cc
diff --git a/chrome/browser/chromeos/arc/arc_auth_service.cc b/chrome/browser/chromeos/arc/arc_auth_service.cc
index c20b7401e98994688138b9c3ba3d02006c883521..e2a8a20970df06dc7bee1df5fc0a23d5e710af32 100644
--- a/chrome/browser/chromeos/arc/arc_auth_service.cc
+++ b/chrome/browser/chromeos/arc/arc_auth_service.cc
@@ -120,9 +120,9 @@ ArcAuthService* ArcAuthService::Get() {
 // static
 void ArcAuthService::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
-  registry->RegisterBooleanPref(
-      prefs::kArcEnabled, false,
-      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+  // TODO(dspaid): Add a syncable default preference so that new
+  // devices get the last opt-in preference.
+  registry->RegisterBooleanPref(prefs::kArcEnabled, false);
   registry->RegisterBooleanPref(prefs::kArcSignedIn, false);
   registry->RegisterBooleanPref(prefs::kArcBackupRestoreEnabled, true);
 }