Go grab it in these last few hours if you haven't. (3 hours 18 minutes as of this writing)
I can even confirm that you can activate it on Origin if you contact support via your EA profile page (I chose live chat). They'll ask you to share your screen to confirm you have the game in steam (since steam doesn't use a serial key for this game) and the customer service elf will then activate it in the Origin account of your choice. Mine even threw in a 15% off voucher for any Origin title. Super nice experience (maybe it's a name thing ... my helper person was named "Vinay" ... quite an obvious homage to GB's own Mr. Caravella, I think)!
Activating Mirror's Edge on Origin is kinda necessary since that's the only place you can get the DLC on the PC.