Back out bug 613659 (for regression bug 998792)

--HG--
rename : layout/reftests/backgrounds/background-size-slice.html => layout/reftests/backgrounds/background-size-continuous.html
rename : layout/reftests/backgrounds/background-size-cover-slice.html => layout/reftests/backgrounds/background-size-cover-continuous.html
rename : layout/reftests/backgrounds/background-size-cover-clone.html => layout/reftests/backgrounds/background-size-cover-each-box.html
rename : layout/reftests/backgrounds/background-size-clone.html => layout/reftests/backgrounds/background-size-each-box.html
Merge backout