Fix crash bug in UnifiedConsentService

The UnifiedConsentService needs a SyncService that is
not NULL, otherwise it will crash.

To fix this, the UnifiedConsentServiceFactory only creates
a UnifiedConsentService if the SyncService is not NULL.

Bug: 872451
Change-Id: I3f7c196273ce5cade9b2f1c88c410eae13569bf7
Reviewed-on: https://chromium-review.googlesource.com/1172301
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582563}

chrome/browser/unified_consent/unified_consent_service_factory.cc

@@ -48,6 +48,8 @@ KeyedService* UnifiedConsentServiceFactory::BuildServiceInstanceFor(
   Profile* profile = Profile::FromBrowserContext(context);
   syncer::SyncService* sync_service =
       ProfileSyncServiceFactory::GetSyncServiceForBrowserContext(profile);
+  if (!sync_service)
+    return nullptr;
 
   if (!IsUnifiedConsentEnabled(profile)) {
     unified_consent::UnifiedConsentService::RollbackIfNeeded(