This fixes trac #1357, which says that some users get annoyed
when the system keeps generating the same color for them, which
would happen if they didn't like #76ce90 and kept picking a
new color for their streams.
(imported from commit 0fdb726aad4009332cc056a5e98bb39e01ef414c)
Instead of splicing up a cloned copy of stream_assignment_colors
every time somebody uses a color, we just rebuild a hash
of used_colors from our subscribed streams when we need to assign
a color, and we avoid calling into stream_color.pick_color() when
a stream already has a color.
This change has a slight functional impact in the situation where
a user unsubscribes some streams during their session, because
we weren't "reclaiming" colors before on unsubscription, but the
simple approach gets that for free.
(imported from commit adf360365bdf1ae9db99c533a0bde62d91f5dfe8)
This is a pure refactoring that mostly just moves code from
subs.js to the new stream_color.js and updates module references
accordingly. In order to prevent introducing some exports,
update_stream_color was given an additional "sub" parameter
and update_stream_sidebar_swatch_color was given an "id"
parameter.
Killed off unused initial_color_fetch var.
(imported from commit b7644ce67f50d31fb46f564d758d661eea776aa6)
