[Sync] Add history delete directive type

chrome/browser/sync/sync_prefs.cc

Index: chrome/browser/sync/sync_prefs.cc
diff --git a/chrome/browser/sync/sync_prefs.cc b/chrome/browser/sync/sync_prefs.cc
index e841eb35c7aa3ac2caa2361a24a8095044c8ac1d..ee9380c513e26f403118ed6e248a58f97282992d 100644
--- a/chrome/browser/sync/sync_prefs.cc
+++ b/chrome/browser/sync/sync_prefs.cc
@@ -120,6 +120,10 @@ void SyncPrefs::SetKeepEverythingSynced(bool keep_everything_synced) {
                             keep_everything_synced);
 }
 
+// TODO(akalin): If encryption is turned on for all data types,
+// history delete directives are useless and so we shouldn't bother
+// enabling them.
+
 syncer::ModelTypeSet SyncPrefs::GetPreferredDataTypes(
     syncer::ModelTypeSet registered_types) const {
   DCHECK(CalledOnValidThread());
@@ -222,6 +226,8 @@ const char* SyncPrefs::GetPrefNameForDataType(syncer::ModelType data_type) {
       return prefs::kSyncSessions;
     case syncer::APP_NOTIFICATIONS:
       return prefs::kSyncAppNotifications;
+    case syncer::HISTORY_DELETE_DIRECTIVES:
+      return prefs::kSyncHistoryDeleteDirectives;
     default:
       break;
   }