Add shutdown notification and service refs to SyncServiceObserver.

ios/chrome/browser/desktop_promotion/desktop_promotion_sync_observer.cc

 // Copyright 2017 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.
 
 #import "ios/chrome/browser/desktop_promotion/desktop_promotion_sync_observer.h"
 
 #include <algorithm>
 #include <memory>
 
 #include "base/metrics/histogram_macros.h"
@@ skipping 20 matching lines @@
     : pref_service_(pref_service), sync_service_(sync_service) {
   DCHECK(pref_service_);
   DCHECK(sync_service_);
   sync_service_->AddObserver(this);
 }
 
 DesktopPromotionSyncObserver::~DesktopPromotionSyncObserver() {
   sync_service_->RemoveObserver(this);
 }
 
-void DesktopPromotionSyncObserver::OnStateChanged() {
+void DesktopPromotionSyncObserver::OnStateChanged(syncer::SyncService* sync) {
   if (desktop_metrics_logger_initiated_ ||
       !sync_service_->GetActiveDataTypes().Has(syncer::PRIORITY_PREFERENCES)) {
     return;
   }
 
   desktop_metrics_logger_initiated_ = true;
   bool done_logging =
       pref_service_->GetBoolean(prefs::kDesktopIOSPromotionDone);
   double last_impression =
       pref_service_->GetDouble(prefs::kDesktopIOSPromotionLastImpression);
@@ skipping 31 matching lines @@
       // If the user saw this promotion type, log that it could be a reason
       // for the signin.
       if ((1 << i) & shown_entrypoints)
         UMA_HISTOGRAM_ENUMERATION("DesktopIOSPromotion.NoSMS.IOSSigninReason",
                                   i, entrypoint_prefixes_count + 1);
     }
   }
   pref_service_->SetBoolean(prefs::kDesktopIOSPromotionDone, true);
   sync_service_->RemoveObserver(this);
 }