Test calling getPropertyValue on computed styles for -webkit-backround-size properties.

getPropertyValue(-webkit-background-size): 10px 20px
getPropertyValue(-webkit-background-size): 10px 10px

Test getting background size of 0.
getPropertyValue(-webkit-background-size): 0px 0px
getPropertyValue(-webkit-background-size): 0px 0px

Test getting initial value of the background size.
getPropertyValue(-webkit-background-size): auto