RFR: 4890732: GZIPOutputStream doesn't support optional GZIP fields [v12]

[Lin Zang]

> 4890732: GZIPOutputStream doesn't support optional GZIP fields

Lin Zang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 17 commits:

 - Merge branch 'master' into gzip-field
 - delete trailing spaces
 - refine code
 - Merge branch 'master' into gzip-field
 - change since version to 18
 - Merge branch 'master' into gzip-field
 - Merge branch 'master' into gzip-field
 - Add api in GZIPInputStream to get header data
 - Merge remote-tracking branch 'upstream/master' into gzip-field
 - remove trailing spaces
 - ... and 7 more: https://git.openjdk.java.net/jdk/compare/c640fe42...196caedb

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Changes: https://git.openjdk.java.net/jdk/pull/3072/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3072&range=11
  Stats: 618 lines in 4 files changed: 568 ins; 26 del; 24 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3072.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3072/head:pull/3072

PR: https://git.openjdk.java.net/jdk/pull/3072