The best solution to this may actually be something like what I am proposing in https://bugs.webkit.org/show_bug.cgi?id=36627.
Skipped in r56578.
Created attachment 64513 [details] Enable editing/selection/shrink-selection-after-shift-pagedown.html This test is not failing anymore (see the chain of bugs: bug #36627 which leads to bug #39854), the latter fixed. The patch just re-enables it.
Comment on attachment 64513 [details] Enable editing/selection/shrink-selection-after-shift-pagedown.html LGTM, r+.
Comment on attachment 64513 [details] Enable editing/selection/shrink-selection-after-shift-pagedown.html Clearing flags on attachment: 64513 Committed r65477: <http://trac.webkit.org/changeset/65477>
All reviewed patches have been landed. Closing bug.