UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10575.58.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36
Platform: 10575.58.0 (Official Build) stable-channel auron_yuna

Steps to reproduce the problem:
1. Enable new system menu in about://flags
2. Wait for a notification to appear

What is the expected behavior?
Have a clear all to dismiss all notification

What went wrong?
No clear all.  Have to dismiss individual notifications

Did this work before? Yes 

Chrome version: 67.0.3396.99  Channel: n/a
OS Version: 10575.58.0
Flash Version: 30.0.0.113 

Old system menu have a clear all button