The 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

the 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.
The JS RB.ReviewRequestFields.CommitListFieldView is responsible for

toggling between the full commit message (if it is longer than a single

line) and the summary.

Ran unit tests.
Ran JS tests.
Uploaded review requests with multiple commits and saw the correct

  commits displayed in the field and in change descriptions.
Uploaded a plain review request and did not see the new field on

  the review request page or change description box.