Chrome: 70.0.3538.7
CrOS: 11021.5.0 eve

1. In chrome://settings, navigate to Device > Touchpad
2. Ensure "Enable tap-to-click" is off
3. Click the "Enable tap-to-click" row or toggle button by quickly depressing and releasing the touchpad

Expected: Button is enabled and tap-to-click is now enabled
Actual: Button is quickly toggled (enabled and then disabled), and tap-to-click is still disabled

Note: This does NOT repro when tapping the row or button using the touchscreen.

This also does NOT repro when clicking the button slowly: depress the touchpad, wait 0.5s, then release the touchpad.

I suspect this is a race condition where a second "click" event is fired due to the touchpad being "tapped" once tap-to-click becomes enabled.