Scrollbar does not appear when using Vimium's "Scroll up" or "Scroll down" command

Bug description

• Demonstrating expected behavior
  • Navigate to ibm.com
  • Use arrow keys, mouse wheel, or spacebar to scroll up and down page
  • Observe that the scrollbar on the right side of the screen appears and moves as the page is scrolled
  • Observe that the scrollbar on the right side of the screen disappears about 1 second after scrolling stops
• Demonstrating Vimium scroll behavior
  • Navigate to ibm.com
  • Use Vimium's scrollDown or scrollUp commands to scroll up or down page
  • Observe that the scrollbar on the right side of the screen does not appear as the page is scrolled

Expected behavior

• Scrollbars appear when using any of Vimium's scrolling commands

Workaround

• Use arrow keys, mouse wheel, or space bar to scroll page to see where on the page the user is currently at

Browser and Vimium version

• Chrome OS 92.0.4515.157
• Vimium 1.67

Impact

• It's not possible to know length of pages when using Vimium's scrolling commands. This is inconvenient when wanting to know where on the page the user is, which is especially needed on long pages and potentially long pages (news articles, comment threads, tutorials, etc).

Reproduce the issue on ibm.com using Vimium's scrollUp and scrollDown commands, then compare the result with arrow-key, mouse-wheel, and spacebar scrolling. Start at the implementation or command entry points for scrollUp and scrollDown; done means the scrollbar appears while either Vimium command scrolls and disappears after scrolling stops.