After we enabled page cache for our port, we found a number of crashes, and unwanted behavior that were caused by our unique scrolling implementation (we try to be as close to what GTK+ expects, which not always maps well to WebCore's expectations, which is why we have quite a bit of platform-specific code). After fixing a number of these, one crash still appears in bug reports fairly frequently. I am attaching a trace.
Created attachment 60651 [details] stack trace
Since we haven't been able to reproduce consistently reproduce this crash, and the traces make it fairly credible that document is NULL, I landed a null check as 62546.
Created attachment 61068 [details] stack trace for a different crash
Created attachment 61070 [details] One more null-check
I'll reuse this bug, since it is tightly related to the other fix that points here.
Comment on attachment 61070 [details] One more null-check OK, hope this one is enough.
Comment on attachment 61070 [details] One more null-check Landed as r63082. Now to try and fix this in a better way.