Implement cancel() API on a Notification object so that script can cancel or ...

chrome/browser/notifications/desktop_notification_service.h

Index: chrome/browser/notifications/desktop_notification_service.h
===================================================================
--- chrome/browser/notifications/desktop_notification_service.h	(revision 30967)
+++ chrome/browser/notifications/desktop_notification_service.h	(working copy)
@@ -52,6 +52,13 @@
       const string16& title, const string16& text, int process_id,
       int route_id, NotificationSource source, int notification_id);
 
+  // Cancels a notification.  If it has already been shown, it will be
+  // removed from the screen.  If it hasn't been shown yet, it won't be
+  // shown.
+  bool CancelDesktopNotification(int process_id,
+                                 int route_id,
+                                 int notification_id);
+
   // Methods to setup and modify permission preferences.
   void GrantPermission(const GURL& origin);
   void DenyPermission(const GURL& origin);