EXPERIMENTAL: put a reminder of the mm rest on the last page at the top. (issue 553400043 by address@hidden)

[nine . fierce . ballads]

There's some stuff here that I already spent time reviewing, and having
to sift through it to find the new stuff is asking a lot.  Would you
mind narrowing this review down to the code for the feature itself?


https://codereview.appspot.com/553400043/