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..7b416053fad2a2ca82ea8186f847b971c0297304 100644
--- a/chrome/common/extensions/api/notifications.idl
+++ b/chrome/common/extensions/api/notifications.idl
@@ -124,31 +124,40 @@ namespace notifications {
 
   interface Functions {
     // Creates and displays a notification.
-    // |notificationId|: Identifier of the notification. If it is empty, this
-    // method generates an id. If it matches an existing notification, this
-    // method first clears that notification before proceeding with the create
-    // operation.
+    // |notificationId|: Identifier of the notification. If not set or empty, an
+    // ID will automatically be generated. If it matches an existing
+    // notification, this method first clears that notification before
+    // proceeding with the create operation.
+    //
+    // The <code>notificationId</code> parameter is required before Chrome 42.
     // |options|: Contents of the notification.
     // |callback|: Returns the notification id (either supplied or generated)
     // that represents the created notification.
-    static void create(DOMString notificationId,
+    //
+    // The callback is required before Chrome 42.
+    static void create(optional DOMString notificationId,
                        NotificationOptions options,
-                       CreateCallback callback);
+                       optional CreateCallback callback);
 
     // Updates an existing notification.
     // |notificationId|: The id of the notification to be updated. This is
     // returned by $(ref:notifications.create) method.
     // |options|: Contents of the notification to update to.
     // |callback|: Called to indicate whether a matching notification existed.
+    //
+    // The callback is required before Chrome 42.
     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);
+    //
+    // The callback is required before Chrome 42.
+    static void clear(DOMString notificationId,
+                      optional ClearCallback callback);
 
     // Retrieves all the notifications.
     // |callback|: Returns the set of notification_ids currently in the system.