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

getPropertyValue(border-spacing): 10px 20px
getPropertyValue(border-spacing): 10px 10px

Test getting border-spacing of 0.
getPropertyValue(border-spacing): 0px 0px
getPropertyValue(border-spacing): 0px 0px

Test getting initial value of the background size.
getPropertyValue(border-spacing): 0px 0px