Destroy AccessContextAuditDatabase on an IO thread

This objects holds an sql::Database, so its destructor can do IO. But
it was destroyed on the UI thread.

Bug: 1141999, 88586
Change-Id: I5ad15deaf7eb3ab5c234d1d4b629dc65216d780b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495351Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820754}

chrome/browser/browsing_data/access_context_audit_service.cc

@@ -54,7 +54,11 @@ void AccessContextAuditService::CookieAccessHelper::FlushCookieRecords() {
 
 AccessContextAuditService::AccessContextAuditService(Profile* profile)
     : clock_(base::DefaultClock::GetInstance()), profile_(profile) {}
-AccessContextAuditService::~AccessContextAuditService() = default;
+
+AccessContextAuditService::~AccessContextAuditService() {
+  // This destructor may do I/O, so destroy it on the database task runner.
+  database_task_runner_->ReleaseSoon(FROM_HERE, std::move(database_));
+}
 
 bool AccessContextAuditService::Init(
     const base::FilePath& database_dir,