Destroy store on task runner. That's where all store operations happen.

components/safe_browsing_db/v4_store.h

 // 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.
 
 #ifndef COMPONENTS_SAFE_BROWSING_DB_V4_STORE_H_
 #define COMPONENTS_SAFE_BROWSING_DB_V4_STORE_H_
 
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/sequenced_task_runner.h"
@@ skipping 158 matching lines @@
   void ApplyUpdate(std::unique_ptr<ListUpdateResponse> response,
                    const scoped_refptr<base::SingleThreadTaskRunner>&,
                    UpdatedStoreReadyCallback);
 
   // If a hash prefix in this store matches |full_hash|, returns that hash
   // prefix; otherwise returns an empty hash prefix.
   virtual HashPrefix GetMatchingHashPrefix(const FullHash& full_hash);
 
   std::string DebugString() const;
 
+  // Schedules the destruction of the V4Store object pointed to by |v4_store|,
+  // on the task runner.
+  static void Destroy(std::unique_ptr<V4Store> v4_store);
+
   // Reads the store file from disk and populates the in-memory representation
   // of the hash prefixes.
   void Initialize();
 
   // Reset internal state.
   void Reset();
 
   // Scheduled after reading the store file from disk on startup. When run, it
   // ensures that the checksum of the hash prefixes in lexicographical sorted
   // order matches the expected value in |expected_checksum_|. Returns true if
@@ skipping 193 matching lines @@
   const base::FilePath store_path_;
   HashPrefixMap hash_prefix_map_;
   const scoped_refptr<base::SequencedTaskRunner> task_runner_;
 };
 
 std::ostream& operator<<(std::ostream& os, const V4Store& store);
 
 }  // namespace safe_browsing
 
 #endif  // COMPONENTS_SAFE_BROWSING_DB_V4_STORE_H_