Pause when clicking anywhere on Pull Request page (BB-9862)

When viewing the diffs in a large pull request, anytime I click anywhere in the screen there is a significant pause, even for operations that don't require any network activity. I've noticed this in particular in Chrome. (The pause on one Pull Request I'm trying in IE11 is probably about a second, whereas it's 3-4 seconds in Chrome.)

Example: Open a large pull request in Chrome. Scroll with the mouse roller down a ways to see that scrolling works fine. Now click in the background and try scrolling immediately. You are unable to scroll for a few seconds.