olivergondza just rejected it a few days ago for 1.596.3, I am guessing because it is too new and did not have the requisite two-week soaking period. That would mean it would have to wait till the next line, something like 1.608.1 (TBD). Bring up on jenkinsci-dev if you feel this needs to be in 1.596.3.
(Do you say that this was a regression from an earlier Jenkins release? My impression was that it was always this way, and Chrome just recently started enforcing the content type. Issues with the regression label deserve special consideration.)
FYI, *.ci.cloudbees.com are already running this patch.
Code changed in jenkins
User: Jesse Glick
Path:
test/src/test/java/hudson/model/ApiTest.java
http://jenkins-ci.org/commit/jenkins/ac80ef27ddd8307d3f57d1185868ac8d92df88a1
Log:
JENKINS-27607Reproduced in test.