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

components/safe_browsing_db/v4_store.cc

Index: components/safe_browsing_db/v4_store.cc
diff --git a/components/safe_browsing_db/v4_store.cc b/components/safe_browsing_db/v4_store.cc
index 81f30ec7cc066c162c19f28f9f5c048ea9fde9ac..299f6d803ede1deae04d214d9e41c77c6d917d32 100644
--- a/components/safe_browsing_db/v4_store.cc
+++ b/components/safe_browsing_db/v4_store.cc
@@ -194,7 +194,9 @@ 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;
@@ -204,6 +206,14 @@ std::string V4Store::DebugString() const {
                             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);
+  }
+}
+
 void V4Store::Reset() {
   expected_checksum_.clear();
   hash_prefix_map_.clear();