Use correct unit enum values for computed clip rectangle
Use correct unit enum values for computed clip rectangle

svn path=/trunk/libcss/; revision=13651

servo/libcss,zhuyadong/libcss,prepare/netsurf_libcss,zhuyadong/libcss,prepare/netsurf_libcss,prepare/netsurf_libcss,zhuyadong/libcss,servo/libcss,servo/libcss