One of the ugly parts of message_list.js is how it re-uses the message objects
from the server to hold handlebars template parameters. These objects are
shared between different message lists and re-renders, but are mutated by the
rendering process. The `dom_id` attribute is normally unset on summary rows,
and should not be used in the template. But when a message comes in with a
`dom_id` from another render, it can end up on the summary row, breaking
`rows.get()`.
(imported from commit ef6af65d5e995dffbd7234547786d6ea861920da)
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)
Kevin Mehall
Waseem Daher
Kevin Mehall
Steve Howell
Scott Feeney
Tim Abbott