Factor out common part of cue-after and cue-before parsers
Factor out common part of cue-after and cue-before parsers

svn path=/trunk/libcss/; revision=7981

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