Try to flush DOMStorage too when ending the browsing session.

content/browser/storage_partition_impl.cc

Index: content/browser/storage_partition_impl.cc
diff --git a/content/browser/storage_partition_impl.cc b/content/browser/storage_partition_impl.cc
index 03b107ac75099480c89d755154db9fd3f7244986..80a6d2eed90cbedb8eee5d0cc049165e2a1ae2ae 100644
--- a/content/browser/storage_partition_impl.cc
+++ b/content/browser/storage_partition_impl.cc
@@ -894,10 +894,13 @@ void StoragePartitionImpl::ClearHttpAndMediaCaches(
   }
 }
 
-void StoragePartitionImpl::Flush() {
+std::vector<scoped_refptr<base::SequencedTaskRunner>>
+StoragePartitionImpl::Flush() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  if (GetDOMStorageContext())
-    GetDOMStorageContext()->Flush();
+  std::vector<scoped_refptr<base::SequencedTaskRunner>> flush_runners;
+  if (dom_storage_context_)
+    flush_runners = dom_storage_context_->Flush();
+  return flush_runners;
 }
 
 void StoragePartitionImpl::ClearBluetoothAllowedDevicesMapForTesting() {