RFR: 8257234 : Add gz option to SA jmap to write a gzipped heap dump [v2]

[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 comments

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1712/files
  - new: https://git.openjdk.java.net/jdk/pull/1712/files/a915f067..909ee247

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=00-01

  Stats: 18 lines in 1 file changed: 1 ins; 3 del; 14 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