Test calling getPropertyValue on computed styles for -webkit-border-image property.

-webkit-border-image: none;
  -webkit-border-image
    getPropertyValue:    none
    getPropertyCSSValue: [object CSSPrimitiveValue]

-webkit-border-image: -webkit-gradient(linear, 0 0, 0 0) 25 25 25 25 stretch stretch;
  -webkit-border-image
    getPropertyValue:    -webkit-gradient(linear, 0 0, 0 0) 25 25 25 25 stretch stretch
    getPropertyCSSValue: [object CSSValue]

-webkit-border-image: -webkit-gradient(linear, 0 0, 0 0) 50 repeat;
  -webkit-border-image
    getPropertyValue:    -webkit-gradient(linear, 0 0, 0 0) 50 50 50 50 repeat repeat
    getPropertyCSSValue: [object CSSValue]

