Scrollbars are missing in Kibana vega visualizations

[anelson-vidscale]

Kibana version: 6.7.3

Elasticsearch version: 6.7.3

Server OS version:

DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.3 LTS"

Browser version:

Google Chrome	78.0.3904.97 (Official Build) (64-bit)

Here is the vega example (this one does not fetch from Elasticsearch):
https://gist.github.com/anelson-vidscale/da3aa82f3842e0655f249a949175ac2e

Expected behavior:

Scrollbars should show up if the vertical space is made small enough that the viz is clipped.

Screenshots (if relevant):

Kibana screenshot

Expected scrollbars show up in the online vega editor

Errors in browser console (if relevant):
There aren't an relevant ones. See the screenshots.

Provide logs and/or server output (if relevant):

Any additional context:

[anelson-vidscale]

And I was able to continue to repro the issue even after removing the height and width from the vega spec:

https://gist.github.com/anelson-vidscale/94504d6d3652078c122d45352347a34f

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

Closing, as this is a duplicate of #22240