Make //content responsible for generating notification Ids

content/public/browser/notification_database_data.cc

Index: content/public/browser/notification_database_data.cc
diff --git a/content/public/browser/notification_database_data.cc b/content/public/browser/notification_database_data.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b942ed93bd9d7dfc45facc920336c65c31fb460d
--- /dev/null
+++ b/content/public/browser/notification_database_data.cc
@@ -0,0 +1,19 @@
+// 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 "content/public/browser/notification_database_data.h"
+
+namespace content {
+
+NotificationDatabaseData::NotificationDatabaseData() = default;
+
+NotificationDatabaseData::NotificationDatabaseData(
+    const NotificationDatabaseData& other) = default;
+
+NotificationDatabaseData& NotificationDatabaseData::operator=(
+    const NotificationDatabaseData& other) = default;
+
+NotificationDatabaseData::~NotificationDatabaseData() = default;
+
+}  // namespace content