When you read messages in a narrow and then un-narrow, collapse
adjacent messages read in the narrow into a summary row that can
be clicked to expand those messages.
Scoped to staging with feature flags.
The implementation of this within our current MessageList is rather ugly.
(imported from commit bcb3a39d8c0c334136fe86318f18ead03f0f50bf)
In a few cases the $.each was doing something imperatively that was
terser and easier to understand by using a different Underscore method,
so a few of these I rewrote.
Some code was using the fact that jQuery sets `this` in the callback to
be the item; I rewrote those to use an explicit parameter.
Some code was using $(some selector).each(callback). I converted these
to _.each($(some selector), callback).
One function, ui.process_condensing, was written to be a jQuery $.each
callback despite being in a totally different module from code using it.
I noticed this and updated the function's args.
(imported from commit bf5922a35f257c168cc09ec1d077415d6ef19a03)
Kevin Mehall
Steve Howell
Tim Abbott
Scott Feeney