Stop showing empty space in the review request box.
On a blank or short review request, the review request box would show

the text areas and then empty space. This was pretty ugly.
We now fill in the remaining space with the last textarea (Testing Done

by default, though this should adapt to custom extension-provided text

fields when those are supported). It will take up the full height,

cleaning up the look.
When the field reaches a point where it'd otherwise extend past those

initial bounds, it will just behave as it did before, autosizing to fit

the content. This ends up feeling pretty natural. As you type in,

say, Description, Testing Done gets pushed down in order to accomodate

Description's size (as it did before), but the bottom now stays

anchored, up until the point where the field hits its natural size and

starts increasing the size of the review request box.

Tested the sizes for the editable <pre> and for CodeMirror. The bottom

of each stayed anchored to the bottom of the container, up until they outgrew it.
This was tested in Chrome, Firefox, and IE10.