This is currently happening in the GTK+ debug bot. There's a test that makes the browser crash due to an assert, hanging the whole process and preventing the rest of the tests from running. When the browser crashes, we correctly handle the pending requests, by completing them with an error. However, if the client tries to send another command we fail to send the message to the browser and the reply is never sent to the client. In the case of the tests, delete session command is sent, but never gets a reply.
Created attachment 332368 [details]
Committed r227674: <https://trac.webkit.org/changeset/227674>