[SPARK-4141] Hide Accumulators column on stage page when no accumulators exist

[mmm]

WebUI

[AmplabJenkins]

Can one of the admins verify this patch?

[JoshRosen]

Jenkins, this is ok to test.

[SparkQA]

Test build #22604 has started for PR 3031 at commit 390893b.

• This patch merges cleanly.

[SparkQA]

Test build #22604 has finished for PR 3031 at commit 390893b.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/22604/
Test FAILed.

[SparkQA]

Test build #22609 has started for PR 3031 at commit 6141cb3.

• This patch merges cleanly.

[mmm]

line dragged over... sorry for the noise

[SparkQA]

Test build #22609 has finished for PR 3031 at commit 6141cb3.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/22609/
Test PASSed.

[JoshRosen]

This looks good to me. It looks like there's now a merge conflict due to me merging Kay's patch, but I'll try to fix it up myself on merge.

[JoshRosen]

Alright, I've fixed the merge conflicts and committed this! Thanks @mmm!