Right now, the diff viewer shows graphs beside each modified file to show whether or not files were added/deleted, how many lines were inserted/changed/deleted, or if there was an error loading the diff information for a given file.
Users were able to depict what the graphs typically mean, however it was desired that tooltips were added for each of the icons to give a detailed description of the change summary for that file.

In my local environment I posted reviews with every type of modification to a file (as well as an erroneous diff of a file) to ensure tooltip was both correct and displaying properly.