What do you use that functionality for? A specific hardware setup that requires the screen to be upside-down? Using a tablet?

I have a projector that is mounted upside down to the celling.

I also have a monitor that is mounted upside down because of the reveal.

seems easy enough to add a 'upside-down' button between the rotate left and rotate right buttons

When we first tested the new display settings, you could make the display go upside down using the rotate buttons. I personally found it really jarring, and I think others did too.

(In reply to comment #3)
> seems easy enough to add a 'upside-down' button between the rotate left and
> rotate right buttons

Yes, this is probably the best option... (Although I am a little hesitant about making this a prominent control - people will inevitably try and it and flip their displays. Very few of them will actually need it.)

*** Bug 719499 has been marked as a duplicate of this bug. ***

Another legitimate use case are tablet laptops like the Lenovo Yoga - see pic:

http://shop.lenovo.com/us/en/landingpage/yoga/yoga-models.html

Most people won't use any of the rotation options, but those who do can figure
out which one to press. Please add this back either by allowing it by clicking
on the rotate buttons multiple times or placing an inverted button in the middle.

Created attachment 263481 [details] [review]
display: Make rotate buttons stay sensitive

It was pointed out that there are some use cases where it is
important to rotate by 180°. The easiest way to allow this is
to keep the rotation buttons sensitive. To alleviate the possible
confusion that the monitor thumbnail looks the same for 0° and
180°, add a label that shows the current rotation.

Created attachment 263482 [details]
rotation label

Created attachment 263561 [details] [review]
display: Add an 'upside-down' button

Turn the rotation buttons into toggle buttons, and add one for
'upside-down'.

Created attachment 263562 [details]
toggle buttons

Created attachment 263577 [details] [review]
display: Use radio buttons

Turn the rotation buttons into radio buttons, and add buttons
for 'rightside up' and 'upside down'.

Created attachment 263578 [details]
radio buttons

Review of attachment 263561 [details] [review]:

Looks good.

Review of attachment 263577 [details] [review]:

As mentioned in IRC, it's not clear what the buttons do, and we lose the direction from the arrows indicating which way the display would "move" when clicked. The toggle flip looks much easier to use to me.

Attachment 263561 [details] pushed as 732d3e0 - display: Add an 'upside-down' button

*** Bug 711309 has been marked as a duplicate of this bug. ***