[Rev 01] RFR: 6657: Add allocation pressure column to Memory and TLAB views

[Jie Kang]

> This patch addresses https://bugs.openjdk.java.net/browse/JMC-6657, which itself is a clone of https://bugs.openjdk.java.net/browse/JMC-5923 that targets the Memory and TLAB pages, rather than the stacktrace view.
> 
> The ItemHistogram and related classes now have support for Percentage columns that divides the aggregate value for items in a row against the aggregate value for all items in the model.
> 
> This is used in the Memory page to show Total Allocation as a Percentage. The TLAB page is modified to be tabbed and contains two ItemHistograms, one for classifying against Threads (previously existed) and one against Top Methods (new). Both also have two new columns: allocations inside and outside TLABs, as a percentage.
> 
> ![tlab-page](https://user-images.githubusercontent.com/5430520/71093691-b2094c00-2177-11ea-9965-f27948964cd3.png)
> TLABs by Top Methods, showcasing sorting by the new percentage column. Together with the stacktrace view, I believe these changes make it easier to see relevant areas of allocation pressure.

The pull request has been updated with 2 additional commits.

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Added commits:
 - 4fd1fa37: Shorten column names with short form for Allocation(s)
 - 375fb831: Shorten column names with short form for Average and Percentage

Changes:
  - all: https://git.openjdk.java.net/jmc/pull/21/files
  - new: https://git.openjdk.java.net/jmc/pull/21/files/9f73e4fd..4fd1fa37

Webrevs:
 - full: https://webrevs.openjdk.java.net/jmc/21/webrev.01
 - incr: https://webrevs.openjdk.java.net/jmc/21/webrev.00-01

  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jmc/pull/21.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/21/head:pull/21

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