[S] Use a weak_factory for V4Database callbacks + test

components/safe_browsing_db/v4_database.cc

Index: components/safe_browsing_db/v4_database.cc
diff --git a/components/safe_browsing_db/v4_database.cc b/components/safe_browsing_db/v4_database.cc
index 5edeb3e9422df61daf2dfe31e5f12d811af37627..8b20a88b3444cf5526903604da78e1f487b3f7b6 100644
--- a/components/safe_browsing_db/v4_database.cc
+++ b/components/safe_browsing_db/v4_database.cc
@@ -91,7 +91,8 @@ V4Database::V4Database(
     std::unique_ptr<StoreMap> store_map)
     : db_task_runner_(db_task_runner),
       store_map_(std::move(store_map)),
-      pending_store_updates_(0) {
+      pending_store_updates_(0),
+      weak_factory_on_io_(this) {
   DCHECK(db_task_runner->RunsTasksOnCurrentThread());
 }
 
@@ -100,6 +101,7 @@ void V4Database::Destroy(std::unique_ptr<V4Database> v4_database) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   V4Database* v4_database_raw = v4_database.release();
   if (v4_database_raw) {
+    v4_database_raw->weak_factory_on_io_.InvalidateWeakPtrs();
     v4_database_raw->db_task_runner_->DeleteSoon(FROM_HERE, v4_database_raw);
   }
 }
@@ -130,8 +132,9 @@ void V4Database::ApplyUpdate(
       if (old_store->state() != response->new_client_state()) {
         // A different state implies there are updates to process.
         pending_store_updates_++;
-        UpdatedStoreReadyCallback store_ready_callback = base::Bind(
-            &V4Database::UpdatedStoreReady, base::Unretained(this), identifier);
+        UpdatedStoreReadyCallback store_ready_callback =
+            base::Bind(&V4Database::UpdatedStoreReady,
+                       weak_factory_on_io_.GetWeakPtr(), identifier);
         db_task_runner_->PostTask(
             FROM_HERE,
             base::Bind(&V4Store::ApplyUpdate, base::Unretained(old_store.get()),
@@ -220,9 +223,10 @@ void V4Database::VerifyChecksum(
   const scoped_refptr<base::SingleThreadTaskRunner> callback_task_runner =
       base::ThreadTaskRunnerHandle::Get();
   db_task_runner_->PostTask(
-      FROM_HERE, base::Bind(&V4Database::VerifyChecksumOnTaskRunner,
-                            base::Unretained(this), callback_task_runner,
-                            db_ready_for_updates_callback));
+      FROM_HERE,
+      base::Bind(&V4Database::VerifyChecksumOnTaskRunner,
+                 weak_factory_on_io_.GetWeakPtr(), callback_task_runner,
+                 db_ready_for_updates_callback));
 }
 
 void V4Database::VerifyChecksumOnTaskRunner(