Add cpu throttling stats.

Docker-DCO-1.1-Signed-off-by: Rohit Jnagal <jnagal@google.com> (github: rjnagal)

cgroups/fs/cpu_test.go

@@ -0,0 +1,40 @@
+package fs
+
+import (
+	"testing"
+)
+
+func TestCpuStats(t *testing.T) {
+	helper := NewCgroupTestUtil("cpu", t)
+	defer helper.cleanup()
+	cpuStatContent := `nr_periods 2000
+	nr_throttled 200
+	throttled_time 42424242424`
+	helper.writeFileContents(map[string]string{
+		"cpu.stat": cpuStatContent,
+	})
+
+	cpu := &cpuGroup{}
+	stats, err := cpu.Stats(helper.CgroupData)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expected_stats := map[string]float64{
+		"nr_periods":     2000.0,
+		"nr_throttled":   200.0,
+		"throttled_time": 42424242424.0,
+	}
+	expectStats(t, expected_stats, stats)
+}
+
+func TestNoCpuStatFile(t *testing.T) {
+	helper := NewCgroupTestUtil("cpu", t)
+	defer helper.cleanup()
+
+	cpu := &cpuGroup{}
+	_, err := cpu.Stats(helper.CgroupData)
+	if err == nil {
+		t.Fatal("Expected to fail, but did not.")
+	}
+}