Beginnings of synchronizing notifications in the notification database.

content/public/browser/platform_notification_service.h

Index: content/public/browser/platform_notification_service.h
diff --git a/content/public/browser/platform_notification_service.h b/content/public/browser/platform_notification_service.h
index afcc31921f340fdc322bcb9ea7c6092848f66591..6c9e50904cf7506b451842b089cd6ae4ef82c32d 100644
--- a/content/public/browser/platform_notification_service.h
+++ b/content/public/browser/platform_notification_service.h
@@ -6,6 +6,7 @@
 #define CONTENT_PUBLIC_BROWSER_PLATFORM_NOTIFICATION_SERVICE_H_
 
 #include <stdint.h>
+#include <set>
 #include <string>
 
 #include "base/callback_forward.h"
@@ -72,6 +73,13 @@ class CONTENT_EXPORT PlatformNotificationService {
   virtual void ClosePersistentNotification(
       BrowserContext* browser_context,
       int64_t persistent_notification_id) = 0;
+
+  // Writes the ids of all currently displaying persistent notifications for the
+  // given |browser_context| to |displayed_notifications|. Returns whether the
+  // platform is able to provide such a set.
+  virtual bool GetDisplayedPersistentNotifications(
+      BrowserContext* browser_context,
+      std::set<std::string>* displayed_notifications) = 0;
 };
 
 }  // namespace content