Merge the hash prefixes from the old store and the additions in the partial

components/safe_browsing_db/v4_database.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.
 
 #include <memory>
 
 #include "base/callback.h"
 #include "base/debug/leak_annotations.h"
 #include "base/files/file_util.h"
 #include "base/memory/ptr_util.h"
@@ skipping 119 matching lines @@
   if (!pending_store_updates_) {
     current_task_runner->PostTask(FROM_HERE, db_updated_callback_);
     db_updated_callback_.Reset();
   }
 }
 
 void V4Database::UpdatedStoreReady(UpdateListIdentifier identifier,
                                    std::unique_ptr<V4Store> new_store) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK(pending_store_updates_);
-  (*store_map_)[identifier] = std::move(new_store);
+  if (new_store) {
+    (*store_map_)[identifier] = std::move(new_store);
+  }
 
   pending_store_updates_--;
   if (!pending_store_updates_) {
     db_updated_callback_.Run();
     db_updated_callback_.Reset();
   }
 }
 
 bool V4Database::ResetDatabase() {
   DCHECK(db_task_runner_->RunsTasksOnCurrentThread());
   bool reset_success = true;
   for (const auto& store_map_iter : *store_map_) {
     if (!store_map_iter.second->Reset()) {
       reset_success = false;
     }
   }
   return reset_success;
 }
 
 std::unique_ptr<StoreStateMap> V4Database::GetStoreStateMap() {
   std::unique_ptr<StoreStateMap> store_state_map =
       base::MakeUnique<StoreStateMap>();
   for (const auto& store_map_iter : *store_map_) {
     (*store_state_map)[store_map_iter.first] = store_map_iter.second->state();
   }
   return store_state_map;
 }
 
 }  // namespace safe_browsing