Creating a review comment on a line of code makes the source jump around

When you select a line of code to create a comment, the opening of the comment box causes the code you are looking at to jump. This is very off-putting.

1. Jump to the side because the gutter columns showing line number, author and changeset id expand. This occurs on Safari and Chrome, but not on Firefox. This occurs on 3.4.6-SNAPSHOT and 3.5.0-SNAPSHOT
#1 is not regression and is moved to the new issue https://jira.atlassian.com/browse/CRUC-6870

2. Vertical jump when the diff is large enough to fill the window. This happens on Safari, Chrome and Firefox. This only occurs on 3.5.0-SNAPSHOT.