RFR: 8255982: Extend BasicJMapTest to test with different GC Heap [v2]

[Lin Zang]

> The implementation of jmap tool depends on the implementation of object iteration by different GC heap.
> This patch extend the BasicJMapTest to cover differet GC Heap.

Lin Zang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into jmap-test
 - 8255982: Extend BasicJMapTest to test with different GC Heap
   
   The implementation of jmap tool depends on the implementation of
   object iteration by different GC heap.
   This patch extend the BasicJMapTest to cover differet GC Heap.

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1094/files
  - new: https://git.openjdk.java.net/jdk/pull/1094/files/f712e6f6..499e75a9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1094&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1094&range=00-01

  Stats: 47904 lines in 413 files changed: 26824 ins; 13713 del; 7367 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1094.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1094/head:pull/1094

PR: https://git.openjdk.java.net/jdk/pull/1094