viviana keith , 27 , reported to be drunk at a nail salon in red rock , texas .
officer ben johnson arrived and found keith walking to her car .
he noticed she was drunk and moved to arrest her , claiming she resisted .
video shows him slamming her to the concrete of the car park .
she was knocked out and suffered a black eye .
charged with dwi with a child younger than 15 and interfering with pubic duties .
incident being investigated but johnson remains on the job .