RFR: 8256450: Add gz option to jmap to write a gzipped heap dump [v4]

[Chris Plummer]

On Thu, 19 Nov 2020 06:16:17 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> This PR add "gz" option to jmap -dump command to support generate gzipped heap dump.
>> 
>> example:
>>       jmap -dump:live,gz=1,file=dump.gz <pid>
>
> Lin Zang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix indentation issue of BasicJmapTest.java

Changes requested by cjplummer (Reviewer).

test/jdk/sun/tools/jmap/BasicJMapTest.java line 270:

> 268:     }
> 269: 
> 270:     private static void verifyDumpFile(File dump, boolean compressed) {

I don't think the `compressed` argument is needed. The rest of the changes look fine.

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PR: https://git.openjdk.java.net/jdk/pull/1251