RFR: 6657: Add allocation pressure column to Memory and TLAB views

[Marcus Hirt]

On Wed, 19 Feb 2020 22:42:48 GMT, Jie Kang <jkang at openjdk.org> wrote:

>> @jiekang - Hi Jie! Did you want to spend some more time looking at ways to clean up the code for the backdrop bars before integrating this?
>
> @thegreystone Hey; sorry a roller-coaster month of sorts. I just made it a little more readable (I hope) and rebased onto latest. I don't have plans to do more for the near future. I will still address any requests with vigor though! I do want to see it through.

![image](https://user-images.githubusercontent.com/16906077/75707067-8994e680-5cbe-11ea-81d1-cfe46b5c4388.png)

I've been thinking of how we can make the naming clearer. What do you think about:

* Avg Alloc in TLABs
* Avg Alloc Outside TLABs
* Total Alloc in TLABs
* Total Alloc Outside TLABs

Reasoning:
* Just saying Avg. TLAB Alloc can be confusing - it's not the TLAB allocation but rather the estimated size of allocations in the TLAB, on average. Also rhymes better with Avg Alloc Outside TLABs. We do explain that it is an estimate in the tooltip, so perhaps we can skip it in the name. We should either have it in both of the inside TLAB columns, or in none of them. 
* I think we can probably drop the contraction periods, but if someone disagrees I don't mind.

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PR: https://git.openjdk.java.net/jmc/pull/21