Add API in developerPrivate to allow/ disallow incognito mode.

chrome/common/extensions/api/developer_private.idl

Index: chrome/common/extensions/api/developer_private.idl
diff --git a/chrome/common/extensions/api/developer_private.idl b/chrome/common/extensions/api/developer_private.idl
index 658111428e7715714675a539c6bf3ae32fc0852b..ec6084e37b09d546d6bb7214d84d0c65eb3fb756 100644
--- a/chrome/common/extensions/api/developer_private.idl
+++ b/chrome/common/extensions/api/developer_private.idl
@@ -98,6 +98,7 @@ namespace developerPrivate {
     PackStatus status;
   };
 
+  callback VoidCallback = void ();
   callback BooleanCallback = void (boolean result);
   callback ItemsInfoCallback = void (ItemInfo[] result);
   callback GetStringsCallback = void (object result);
@@ -139,6 +140,11 @@ namespace developerPrivate {
                        boolean enable,
                        optional VoidCallback callback);
 
+    // Allow / Disallow item with |item_id| in incognito mode.
+    static void allowIncognito(DOMString item_id,
+                               boolean allow,
+                               VoidCallback callback);
+
     // Load a user selected unpacked item
     static void loadUnpacked(optional VoidCallback callback);