On fast networks where page transitions are quick, such as local dev in
most cases, the progress bar should not render. This leads to a constant
flashing of the progress bar at the top of the screen and does not
provide any value.
The fix is to add a delay to the initial rendering of the progress bar,
and only show if the transition takes longer than _n_ milliseconds. This
value can be adjusted as needed, but right now is set to 150ms.
Introduced in #9275.
de68ef4548