Add support for content labels on commit

Add commit options which allow for setting labels on commit.
Prevents potential race between garbage collector reading labels
after commit and labels getting set.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

content/content.go

@@ -90,7 +90,7 @@ type Writer interface {
 
 	// Commit commits the blob (but no roll-back is guaranteed on an error).
 	// size and expected can be zero-value when unknown.
-	Commit(size int64, expected digest.Digest) error
+	Commit(size int64, expected digest.Digest, opts ...Opt) error
 
 	// Status returns the current state of write
 	Status() (Status, error)
@@ -107,3 +107,13 @@ type Store interface {
 	IngestManager
 	Ingester
 }
+
+// Opt is used to alter the mutable properties of content
+type Opt func(*Info) error
+
+func WithLabels(labels map[string]string) Opt {
+	return func(info *Info) error {
+		info.Labels = labels
+		return nil
+	}
+}