RFR: 8257234 : Add gz option to SA jmap to write a gzipped heap dump [v19]

[Lin Zang]

> 8257234 : Add gz option to SA jmap to write a gzipped heap dump

Lin Zang has updated the pull request incrementally with one additional commit since the last revision:

  refine code in test.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1712/files
  - new: https://git.openjdk.java.net/jdk/pull/1712/files/47d93a9d..6fe0f79b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=18
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=17-18

  Stats: 6 lines in 1 file changed: 3 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1712.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1712/head:pull/1712

PR: https://git.openjdk.java.net/jdk/pull/1712