WebContext::registerSchemeForCustomProtocol() uses sendToNetworkingProcess() to send the message to the appropriate networking process. In the case of using web process, sendToNetworkingProcess() first checks if there's already a web process, doing nothing otherwise, but when using the network process it assumes there's already a network process. In both cases it's safe to do nothing, because the schemes will be passed as creation parameters to the process when launched.
Created attachment 220227 [details]
Committed r161416: <http://trac.webkit.org/changeset/161416>