Showing a "(i)" info icon (using Font Awesome) on the right-hand side of a row's summary column when hovering over the row or when the focus is on some child of the row. The infobox should only be popped up when hovering over that icon, or when tabbing to it and pressing Space, Enter, Up, or Down.
Improving keyboard accessibility in the infobox. When opening the infobox via keyboard, focus should move to the infobox. The branch, timestamp, and description fields will also be focusable.
Tabbing out of the infobox or pressing Escape should close the infobox.

[aria-expanded="true"] keeps icon when infobox open.
Add info-icon & add key accessibility to icon:

_onTargetKeyDown($target, InfoboxViewType, evt)  will display the infobox by pressing UP, DOWN, ENTER, SPACE key while the info-icon is focused.

_onInfoboxKeyDown(evt)  will hidden the infobox by pressing ESCAPE key while the infobox or it's children are focused.
tabindex="0" makes branch & timestamp, and description area focusable.
Make branch, timestamp, and description area accessibly by keydown:

_onHoverItemKeyDown(evt) will display the hover details for the branch and timestamp by pressing UP, DOWN, ENTER, SPACE key while the item is focused. This will hide the hover details for the item by pressing ESCAPE key while the item is focused.

_onScrollableKeyDown(evt) will turn off the padding so the scrollbar has room by pressing UP, DOWN, ENTER, SPACE key while the item is focused. This will re-enable the padding where the scrollbar would be by pressing ESCAPE key while the item is focused.

Manually Tested on Firefox, Chrome, and Safari.