Add a function which is called before every render to
get the number of items it can render. This can be used by
instance to load custom number of items as per its state.
We allow ListWidget instances to pass functions in opts that can
be called after scrolling to determine when to render.
Also, allow a callback function to be called pre render.
This improves the UX of creating a stream for atleast 1000+ users
realm by showing the the stream creation form much faster than
before.
Search, user addition, scrolling worked smoothly on 15k+
users realm as tested on dev setup.
Also, simplebar is used to replace the default scrollbar.
Fixes#16805
Now when we want to measure how long a block
of code takes to execute, we just wrap it with
`blueslip.measure_time`, instead of the awkward
idiom from my original commit of getting a callback
function.
My rationale for the original scheme was that I
wanted to minimize diffs and avoid changing
`const` to `let` in a few cases, but I believe
now that the function wrapper is nicer.
In a few cases I just removed the blueslip timing
code, since I was able to confirm on czo that
the times were pretty minimal.
Aman Agrawal
Anders Kaseorg
Steve Howell
Rohitt Vashishtha