Addonds might implement newChannel() from nsIProtocolHandler. Since we are adding newChannel2 to nsIProtocolHandler, addons probably have no implemented that function. Hence we have to provide a shim (nsSecurityCheckingWrapperChannel) which allos to call newChannel in case newChannel2 is not implemented. > The constructor for this class would take an nsIChannel instance and forward all calls to that nsIChannel. Later, once we move security checks into asyncOpen, we can also reuse that shim functionality in case asyncOpen2 (which does security checks) is not implemented by the addon.
Marking this as a duplicate of: 1120487