Bug 550426 - Use background-position-x/y when detecting scroll-linked effects. r=dbaron

MozReview-Commit-ID: 6qDFcaEBYEF

--HG--
extra : rebase_source : b1055f871651f9dc71ba4e34f16afb06bf871b84

layout/style/nsDOMCSSDeclaration.cpp

@@ -80,6 +80,8 @@ nsDOMCSSDeclaration::SetPropertyValue(const nsCSSProperty aPropID,
 {
   switch (aPropID) {
     case eCSSProperty_background_position:
+    case eCSSProperty_background_position_x:
+    case eCSSProperty_background_position_y:
     case eCSSProperty_transform:
     case eCSSProperty_top:
     case eCSSProperty_left: