Chrome Version       : 65.0.3325.181
URLs (if applicable) : chat.google.com
Other browsers tested:
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari: 
    Firefox:
       Edge:

What steps will reproduce the problem?
User changed timezone from CST to PDT (unsure why user was in CST and not CDT) but Date API doesn't seem to reflect the time change.
Few things to note:
- Spun up app in another tab and it didn't have the TZ issue. 
- Opened other apps (gmail.com) in the bad tab and it had the same TZ problem
- User reported that `new Date()` on bad tab reports `Fri Apr 06 2018 18:58:04 GMT+0000 (UTC)` when in PDT
- User reported that `Intl.DateTimeFormat().resolvedOptions().timeZone` returns `America/Los_Angeles`

I asked the reporter NOT to close the bad tab for further diagnostics.

What is the expected result?


What happens instead?


Please provide any additional information below. Attach a screenshot if
possible.