func newContentMemFile(src, dst string, hdr *tar.Header) *contentMemFile {
	return &contentMemFile{
		src: src,
		dst: dst,
		hdr: hdr,
	}
}
newContentMemFile inits a new contentMemFile.
package snapshot
import (
	"archive/tar"
	"fmt"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
	"github.com/uber/makisu/lib/log"
	"github.com/uber/makisu/lib/pathutils"
	"github.com/uber/makisu/lib/tario"
)
type memFile interface {
	updateMemFS(tree *memFSNode) error
	commit(w *tar.Writer) error
}
type contentMemFile struct {
	src string  
	dst string  
	hdr *tar.Header
}