As a user, I would like the background page to be prevented from scrolling when using the side-by-side diff view. (BB-11472)

Browser: Chrome
Bitbucket -> Pull Request -> Side by Side diff
When scrolling the side-by-side diff view, if the diff file ends, the
background page starts scrolling. This is really inconvenient because when
the side-by-side diff is closed, you return to the pull request page but it
would have scrolled and you won't be where you had left. Extremely
inconvenient for large pull requests.