Recently I've made 2 backports of my own fix of https://bugs.openjdk.java.net/browse/JDK-8257414 using Scara to jdk11u and jdk13u.

In case of jdk13u I remained the author of the fix. I followed the guideline for the backports from git to git repositories described here:
https://wiki.openjdk.java.net/display/SKARA/Backports#Backports-Reviewingbackports

In case of jdk11u the commiter became the author of the fix. I used the command for the backports from git to mercurial repositories described here:
https://wiki.openjdk.java.net/display/SKARA/git-hg-export
"git-hg-export exports a commit to standard out on a format suitable for hg import. git-hg-export will also reformat the commit message to the format that is used by OpenJDK Mercurial repositories. These two properties makes it easy to export a commit from an OpenJDK Git repository and import the patch into an OpenJDK Mercurial repository (with correct commit metadata such as author, timestamp and commit message preserved)."
I made the following:
git hg-export d3398324e9c3944d2f1558ff1becea9ed1d4e8a2 > 8257414.patch
hg import 8257414.patch
The patch is the same in case of: git hg-export d3398324