How to find a file with a specific extension (.aidl) ?

I need to change an .aidl file using my plugin but I am having trouble getting files with the .aidl extension since it's not a standard type and thereby I can't use it in this:

Collection<VirtualFile> xmlFiles = FileBasedIndex.getInstance().getContainingFiles(
        FileTypeIndex.NAME,
        XmlFileType.INSTANCE, //Should be Aidl here
        GlobalSearchScope.allScope(getProject()));

Any idea on how to address this issue?