In bug 47938 <http://trac.webkit.org/changeset/70097>, we added support for tracking the unreachable URL in the UI process in WebFrameProxy. However, as soon as you start loading a new URL, any previous unreachable URL is lost. If you cancel loading the new page, the previous page is still shown, but it no longer has an unreachable URL.
Created attachment 92121 [details]
Committed r85655: <http://trac.webkit.org/changeset/85655>