Update wl_notificationtimestamp when updating Flow page

Requires Iae213b87706c447b880244711e7747954423bb69 to be merged
in core first.

There may still be interaction issues with if we want to be doing
the watchlist for the Topic or the Board, but that can be worked
out separately.

Bug: 66876
Change-Id: I14320b747d16b7be652da05bda59fdf4e8eece81
Merge "Update wl_notificationtimestamp when updating Flow page"