support IUnit of Allocation Rate

[Liu, Xin]

Hi, Developers,

I am new for the codebase of Java mission control. I would like to add
allocation Rate in Summary page(JMC-7301).

I manage to extend aggregators ALLOC_INSIDE_TLAB_SUM and
ALLOC_OUTSIDE_TLAB_SUM. The duration is known from TlabPage::visibleRange.

The biggest challenge is to align with the new unit. IUnit of Allocation
Rate is B/s. I haven't found similar IUnit like that. Is there a way to
derive B/s from Memory?

To display the correct unit of allocation rate, I create a new
LinearKindOfQuantity "memory bandwidth". The only difference of it from
memory is that its atom unit is B/s.

Here is my attempt. sorry it looks awful. Any suggest to make it more
elegant?

https://github.com/navyxliu/jmc/commit/b3cd19b1b6bb5cb93241b4dbb8086a6305fe4023#diff-d740b28fe16b17f85bf34790e5afc60eb0d2f39d7827f894184713430d74131bR793


thanks,
--lx