Add a comment: Any new lists must already be supported by the SB server

components/safe_browsing_db/v4_local_database_manager.cc

 // Copyright 2016 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.
 
 // This file should not be build on Android but is currently getting built.
 // TODO(vakh): Fix that: http://crbug.com/621647
 
 #include "components/safe_browsing_db/v4_local_database_manager.h"
 
 #include <vector>
@@ skipping 58 matching lines @@
                SB_THREAT_TYPE_BINARY_MALWARE_URL),
       ListInfo(kSyncAlways, "ChromeExtMalware.store", GetChromeExtMalwareId(),
                SB_THREAT_TYPE_EXTENSION),
       ListInfo(kSyncOnlyOnChromeBuilds, "ChromeUrlClientIncident.store",
                GetChromeUrlClientIncidentId(),
                SB_THREAT_TYPE_BLACKLISTED_RESOURCE),
       ListInfo(kSyncNever, "", GetChromeUrlApiId(), SB_THREAT_TYPE_API_ABUSE),
       ListInfo(kSyncOnlyOnChromeBuilds, "UrlSubresourceFilter.store",
                GetUrlSubresourceFilterId(), SB_THREAT_TYPE_SUBRESOURCE_FILTER),
   });
+  // NOTE(vakh): IMPORTANT: Please make sure that the server already supports
+  // any list before adding it to this list otherwise the prefix updates break
+  // for all Canary users.
 }
 
 // Returns the severity information about a given SafeBrowsing list. The lowest
 // value is 0, which represents the most severe list.
 ThreatSeverity GetThreatSeverity(const ListIdentifier& list_id) {
   switch (list_id.threat_type()) {
     case MALWARE_THREAT:
     case SOCIAL_ENGINEERING_PUBLIC:
     case MALICIOUS_BINARY:
       return 0;
@@ skipping 650 matching lines @@
                             db_updated_callback_);
 }
 
 bool V4LocalDatabaseManager::AreStoresAvailableNow(
     const StoresToCheck& stores_to_check) const {
   return enabled_ && v4_database_ &&
          v4_database_->AreStoresAvailable(stores_to_check);
 }
 
 }  // namespace safe_browsing