Chrome Version       : 50.0.2661.75 (Official Build) (64-bit)
URLs (if applicable) : N/A
Other browsers tested: N/A

What steps will reproduce the problem?
(1) Open Dev tools
(2) Go to Experiments Tab
(3) "Collapsbile row groups in Timeline"

What is the expected result?

Collapsible row groups in Timeline

What happens instead?

Collapsbile row groups in Timeline

System Config: Ubuntu 14.04.4 LTS