We have seen crash traces that indicate the frame is being detached from the document while stopping a load, leading to nullptr dereferences and crashes. Other loading code anticipates the possibility the the frame is nullptr. Since these crashes are happening at the tail end of the load termination, when attempting to notify the now-detached client that the load was stopped, we should probably just recognize this is happening and avoid the dereference.
Created attachment 302163 [details] Patch
Comment on attachment 302163 [details] Patch r=me. It's sad we can't have a test for this.
Committed r212667: <http://trac.webkit.org/changeset/212667>
<rdar://problem/29852056>