Introduce the NotificationIdGenerator in //content.

content/browser/notifications/notification_id_generator.h

+// Copyright 2015 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.
+
+#ifndef CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_ID_GENERATOR_H_
+#define CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_ID_GENERATOR_H_
+
+#include <stdint.h>
+#include <string>
+
+#include "content/common/content_export.h"
+
+class GURL;
+
+namespace content {
+
+class BrowserContext;
+
+// Generates deterministic notification ids for Web Notifications.
+//
+// The notification id must be deterministic for a given browser context, origin
+// and tag, when the tag is non-empty, or unique for the given notification when

[johnme, 2015/05/27 18:18:35]

Please clearly explain that calling new Notification() or swr.showNotification()
with the same (non-empty) tag as an existing notification is considered to
update the existing notification 'object', hence these will have the same id,
since this might otherwise be surprising to people who expect "new
Notification(..)" to create a different notification 'object'.

[Peter Beverloo, 2015/05/28 12:51:44]

Done.

+// the tag is empty. For non-persistent notifications, the uniqueness will be
+// based on the render process id. For persistent notifications, the generated
+// id will be globally unique for the lifetime of the notification database.
+//
+// The notification id will be used by the notification service for determining
+// when to replace notifications, and as the unique identifier when a
+// notification has to be closed programmatically.
+//
+// It is important to note that, for persistent notifications, the generated
+// notification id can outlive the browser process responsible for creating it.
+class CONTENT_EXPORT NotificationIdGenerator {
+ public:
+  NotificationIdGenerator(BrowserContext* browser_context,
+                          int render_process_id);
+  ~NotificationIdGenerator();
+
+  // Generates an id for a persistent notification given the notification's
+  // origin, tag and persistent notification id. The persistent notification id
+  // will have been created by the persistent notification database.
+  std::string GenerateForPersistentNotification(
+      const GURL& origin,
+      const std::string& tag,
+      int64_t persistent_notification_id) const;
+
+  // Generates an id for a non-persistent notification given the notification's
+  // origin, tag and non-persistent notification id. The non-persistent
+  // notification id will have created by the renderer with |render_process_id|.
+  std::string GenerateForNonPersistentNotification(
+      const GURL& origin,
+      const std::string& tag,
+      int non_persistent_notification_id) const;
+
+ private:
+  // The NotificationMessageFilter that owns |this| will outlive the context.
+  BrowserContext* browser_context_;
+
+  int render_process_id_;
+};
+
+}  // namespace context
+
+#endif  // CONTENT_BROWSER_NOTIFICATIONS_NOTIFICATION_ID_GENERATOR_H_