UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36

Steps to reproduce the problem:
(1) Use a browser for several days without restarting.
(2) In the omnibox, type "amazon.com" (or any other string) quickly in less than a second.
(3) Observe that it takes more than 5 seconds (>500ms per character) for the omnibox to catch up.

Other details
- tell me if the lag seems to occur for all input or just certain things you type.
Occurs for all input, both web addresses and queries, from the very first character.

- tell me if the omnibox get slower over time as Chrome runs or stays roughly the same (started out slow and stays that way)
Quitting and restarting Chrome makes the omnibox fast again.  Also, opening a new incognito window creates an omnibox that is fast, no restart needed.

- tell me if the problem occurs in a new / empty profile
Have not tried to use chrome heavily for several days starting with an empty profile.

- try disabling all extensions.  does the lag still occur?
Yes, all extensions disabled, lag still occurs.

- if you change your default search engine to something besides Google, does it still happen?
Yes, default search engine changed to Bing and Ask, lag still occurs.

What is the expected behavior?
Omnibox should start fast and stay fast.

What went wrong?
Omnibox slows down dramatically after several days of browser use.

Did this work before? Yes With similar browser use, did not observe "increasingly slow omnibox" before 2018

Chrome version: 67.0.3396.99  Channel: n/a
OS Version: OS X 10.13.6
Flash Version: