Kubelet: record the initial pod processing latency

Add a new latency metric for the time from seeing the pod for the first time
to starting a pod worker for it.

Also, change PodStartLatency to include this initial processing latency.

pkg/kubelet/types/types.go

@@ -16,7 +16,10 @@ limitations under the License.
 
 package types
 
-import "net/http"
+import (
+	"net/http"
+	"time"
+)
 
 // DockerID is an ID of docker container. It is a type to make it clear when we're working with docker container Ids
 type DockerID string
@@ -24,3 +27,32 @@ type DockerID string
 type HttpGetter interface {
 	Get(url string) (*http.Response, error)
 }
+
+// Timestamp wraps around time.Time and offers utilities to format and parse
+// the time using RFC3339Nano
+type Timestamp struct {
+	time time.Time
+}
+
+// NewTimestamp returns a Timestamp object using the current time.
+func NewTimestamp() *Timestamp {
+	return &Timestamp{time.Now()}
+}
+
+// ConvertToTimestamp takes a string, parses it using the RFC3339Nano layout,
+// and converts it to a Timestamp object.
+func ConvertToTimestamp(timeString string) *Timestamp {
+	parsed, _ := time.Parse(time.RFC3339Nano, timeString)
+	return &Timestamp{parsed}
+}
+
+// Get returns the time as time.Time.
+func (t *Timestamp) Get() time.Time {
+	return t.time
+}
+
+// GetString returns the time in the string format using the RFC3339Nano
+// layout.
+func (t *Timestamp) GetString() string {
+	return t.time.Format(time.RFC3339Nano)
+}