Test build #35222 has finished for PR 6896 at commit 89251d8.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class SerializableConfiguration(@transient var value: Configuration) extends Serializable
  • class SerializableJobConf(@transient var value: JobConf) extends Serializable

It's a developer API, but is it worth hiding at this point? does it cause problems?

@srowen, Thank you for your comment.
Yes, it's a developer API for getters, but I think setters should not open for developers like other setters of this class because if they are open, task metrics might be overwritten by developers.

A lot of similar stuff was done in 1.3 in SPARK-3288: 3453d57

Seems consistent, yeah. @rxin are you OK with it? just because you committed this particular line last.

LGTM. Merging. Thanks!