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

components/safe_browsing_db/v4_store.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 "base/base64.h"
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
@@ skipping 176 matching lines @@
   DCHECK(state_.empty());
 
   StoreReadResult store_read_result = ReadFromDisk();
   RecordStoreReadResult(store_read_result);
 }
 
 V4Store::V4Store(const scoped_refptr<base::SequencedTaskRunner>& task_runner,
                  const base::FilePath& store_path)
     : store_path_(store_path), task_runner_(task_runner) {}
 
-V4Store::~V4Store() {}
+V4Store::~V4Store() {
+  DCHECK(task_runner_->RunsTasksOnCurrentThread());
+}
 
 std::string V4Store::DebugString() const {
   std::string state_base64;
   base::Base64Encode(state_, &state_base64);
 
   return base::StringPrintf("path: %" PRIsFP "; state: %s",
                             store_path_.value().c_str(), state_base64.c_str());
 }
 
+// static
+void V4Store::Destroy(std::unique_ptr<V4Store> v4_store) {
+  V4Store* v4_store_raw = v4_store.release();
+  if (v4_store_raw) {
+    v4_store_raw->task_runner_->DeleteSoon(FROM_HERE, v4_store_raw);
+  }

[Scott Hess - ex-Googler, 2016/10/18 02:57:01]

OK, yeah, same pattern as V4Database, makes sense.

+}
+
 void V4Store::Reset() {
   expected_checksum_.clear();
   hash_prefix_map_.clear();
   state_ = "";
 }
 
 ApplyUpdateResult V4Store::ProcessPartialUpdateAndWriteToDisk(
     const std::string& metric,
     const HashPrefixMap& hash_prefix_map_old,
     std::unique_ptr<ListUpdateResponse> response) {
@@ skipping 592 matching lines @@
                << "; expected: " << expected_checksum_b64
                << "; store: " << *this;
 #endif
       return false;
     }
   }
   return true;
 }
 
 }  // namespace safe_browsing