[NTP Snippets] Persist the set of snippets in a pref

ios/chrome/browser/prefs/browser_prefs.mm

Index: ios/chrome/browser/prefs/browser_prefs.mm
diff --git a/ios/chrome/browser/prefs/browser_prefs.mm b/ios/chrome/browser/prefs/browser_prefs.mm
index aafd2e14006f363be7f19312844fb8fb74159524..3bcb2bbc3e2382a8a6bbf449e753b2cbe88413c8 100644
--- a/ios/chrome/browser/prefs/browser_prefs.mm
+++ b/ios/chrome/browser/prefs/browser_prefs.mm
@@ -11,6 +11,7 @@
 #include "components/flags_ui/pref_service_flags_storage.h"
 #include "components/gcm_driver/gcm_channel_status_syncer.h"
 #include "components/network_time/network_time_tracker.h"
+#include "components/ntp_snippets/ntp_snippets_service.h"
 #include "components/omnibox/browser/zero_suggest_provider.h"
 #include "components/password_manager/core/browser/password_manager.h"
 #include "components/pref_registry/pref_registry_syncable.h"
@@ -85,6 +86,7 @@ void RegisterBrowserStatePrefs(user_prefs::PrefRegistrySyncable* registry) {
   gcm::GCMChannelStatusSyncer::RegisterProfilePrefs(registry);
   HostContentSettingsMap::RegisterProfilePrefs(registry);
   HttpServerPropertiesManagerFactory::RegisterProfilePrefs(registry);
+  ntp_snippets::NTPSnippetsService::RegisterProfilePrefs(registry);
   password_manager::PasswordManager::RegisterProfilePrefs(registry);
   PrefProxyConfigTrackerImpl::RegisterProfilePrefs(registry);
   sync_driver::SyncPrefs::RegisterProfilePrefs(registry);