CommitListField renders the summaries (and authors if they differ
from the review request submitter) of the commits that make up a
multi-commit review request. This field has been added to a new
ExtraFieldSet, which exists below the
MainFieldSet. This is due to
RB.ReviewRequestEditorView expecting the last field in the main
field set to be an editable text field and working around this
limitation was more complex and convoluted than adding a new fieldset.
RB.ReviewRequestFields.CommitListFieldView is responsible for
toggling between the full commit message (if it is longer than a single
line) and the summary.