Mark create/update/clear callbacks of notification API as optional

chrome/common/extensions/api/notifications.idl

Index: chrome/common/extensions/api/notifications.idl
diff --git a/chrome/common/extensions/api/notifications.idl b/chrome/common/extensions/api/notifications.idl
index fb1fe65b98977bd6430b043c8f92f0af55287492..89a852536c8d491d213b975118582f3fc51164aa 100644
--- a/chrome/common/extensions/api/notifications.idl
+++ b/chrome/common/extensions/api/notifications.idl
@@ -133,7 +133,7 @@ namespace notifications {
     // that represents the created notification.
     static void create(DOMString notificationId,
                        NotificationOptions options,
-                       CreateCallback callback);
+                       optional CreateCallback callback);
 
     // Updates an existing notification.
     // |notificationId|: The id of the notification to be updated. This is
@@ -142,13 +142,14 @@ namespace notifications {
     // |callback|: Called to indicate whether a matching notification existed.
     static void update(DOMString notificationId,
                        NotificationOptions options,
-                       UpdateCallback callback);
+                       optional UpdateCallback callback);
 
     // Clears the specified notification.
     // |notificationId|: The id of the notification to be cleared. This is
     // returned by $(ref:notifications.create) method.
     // |callback|: Called to indicate whether a matching notification existed.
-    static void clear(DOMString notificationId, ClearCallback callback);
+    static void clear(DOMString notificationId,
+                      optional ClearCallback callback);
 
     // Retrieves all the notifications.
     // |callback|: Returns the set of notification_ids currently in the system.