Keyboard shortcut doesn't work for "Start review" button

Issue Summary

This is reproducible on Data Center: no

Steps to Reproduce

1. Begin adding a comment to a pull request
2. Attempt to use the keyboard shortcut Cmd-Enter or Ctrl-Enter to engage the "Start review" button

Expected Results

Using the keyboard shortcut Cmd-Enter or Ctrl-Enter while typing a comment is expected  to be the equivalent of clicking on the "Start review" button. It should start the review.

Actual Results

Nothing happens - the keyboard shortcut does not cause the button to be clicked. This is inconsistent with the previous behavior for the "Save" button for comments (prior to the introduction of the Batched Comments feature).

Workaround

Instead of using a keyboard shortcut, click "Start review" with the mouse.