Related to https://bugs.webkit.org/show_bug.cgi?id=205650, but it also happens with AC mode.
Another regression from https://github.com/WebKit/webkit/commit/94d2fcd0c2eb2399b31253290153676de5cf21ee
Is it possible to somehow not immediately blank the drawing area on PSON and show the previous contents until there's something new to draw (which the new process won't do because layer tree state will be frozen)?
Well this seems bad.
I guess it's related, while loading a new page, WebKitGTK randomly flashes.