Daisy chain two dell UltraSharp u2414h to MacBook Air (mid 2012)?
DisplayPort protocol doesn't chain. It is a one to one technology, so you need two ports on the Mac. 

Thunderbolt does chain, so you could have one Thunderbolt Display and then plug a second monitor (either Thunderbolt or Mini DisplayPort) into the first monitor's second connector. 

That works very well.