Add freezer stats

This one is a problem because the most useful stat is a string and not a
float like verything else.  We may have to change the return type
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

cgroups/fs/freezer.go

@@ -1,7 +1,13 @@
 package fs
 
 import (
+	"fmt"
 	"github.com/dotcloud/docker/pkg/cgroups"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
 )
 
 type freezerGroup struct {
@@ -20,5 +26,37 @@ func (s *freezerGroup) Remove(d *data) error {
 }
 
 func (s *freezerGroup) Stats(d *data) (map[string]float64, error) {
-	return nil, ErrNotSupportStat
+	var (
+		paramData = make(map[string]float64)
+		params    = []string{
+			"parent_freezing",
+			"self_freezing",
+			// comment out right now because this is string "state",
+		}
+	)
+
+	path, err := d.path("freezer")
+	if err != nil {
+		return nil, err
+	}
+
+	for _, param := range params {
+		f, err := os.Open(filepath.Join(path, fmt.Sprintf("freezer.%s", param)))
+		if err != nil {
+			return nil, err
+		}
+		defer f.Close()
+
+		data, err := ioutil.ReadAll(f)
+		if err != nil {
+			return nil, err
+		}
+
+		v, err := strconv.ParseFloat(strings.TrimSuffix(string(data), "\n"), 64)
+		if err != nil {
+			return nil, err
+		}
+		paramData[param] = v
+	}
+	return paramData, nil
 }