Do not sync the ARC++ opt-in preference.

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 625e85dd38825c6674e4e399009c6ea4a5e71e07..476ca3808a905c6d49cc96efc72cf765921277ab 100644
--- a/chrome/browser/chromeos/arc/arc_auth_service.cc
+++ b/chrome/browser/chromeos/arc/arc_auth_service.cc
@@ -155,9 +155,9 @@ ArcAuthService* ArcAuthService::Get() {
 // static
 void ArcAuthService::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
-  registry->RegisterBooleanPref(
-      prefs::kArcEnabled, false,
-      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+  // TODO(dspaid): Implement a mechanism to allow this to sync on first boot
+  // only.
+  registry->RegisterBooleanPref(prefs::kArcEnabled, false);
   registry->RegisterBooleanPref(prefs::kArcSignedIn, false);
   registry->RegisterBooleanPref(prefs::kArcBackupRestoreEnabled, true);
   registry->RegisterBooleanPref(prefs::kArcLocationServiceEnabled, true);
@@ -520,6 +520,9 @@ void ArcAuthService::OnOptInPreferenceChanged() {
   DCHECK(thread_checker.Get().CalledOnValidThread());
   DCHECK(profile_);
 
+  // TODO(dspaid): Move code from OnSyncedPrefChanged into this method.
+  OnSyncedPrefChanged(prefs::kArcEnabled, IsArcManaged());
+
   const bool arc_enabled = IsArcEnabled();
   FOR_EACH_OBSERVER(Observer, observer_list_, OnOptInEnabled(arc_enabled));