Squash memory leak
Squash memory leak

svn path=/trunk/libcss/; revision=6438

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