Remove redundant __name__ label from protobuf output.

Change-Id: I72d5dbccb0325d6edf7abe5bca88dc5a6001029c

prometheus/registry.go

@@ -281,6 +281,13 @@ func (r *registry) dumpDelimitedPB(w io.Writer) {
 		container.Metric.dumpChildren(f)
 
 		for name, value := range container.BaseLabels {
+			if model.LabelName(name) == model.MetricNameLabel {
+				// The name is already in MetricFamily.
+				continue
+				// TODO: Once JSON is history, do not anymore
+				// add the __name__ label to BaseLabels and
+				// then remove this check.
+			}
 			p := &dto.LabelPair{
 				Name:  proto.String(name),
 				Value: proto.String(value),

prometheus/registry_test.go

@@ -229,10 +229,6 @@ func testHandler(t tester) {
 							Name:  proto.String("externalbasename"),
 							Value: proto.String("externalbasevalue"),
 						},
-						&dto.LabelPair{
-							Name:  proto.String("__name__"),
-							Value: proto.String("externalname"),
-						},
 					},
 					Counter: &dto.Counter{
 						Value: proto.Float64(1),
@@ -272,10 +268,6 @@ func testHandler(t tester) {
 						Name:  proto.String("basename"),
 						Value: proto.String("basevalue"),
 					},
-					&dto.LabelPair{
-						Name:  proto.String("__name__"),
-						Value: proto.String("name"),
-					},
 				},
 				Counter: &dto.Counter{
 					Value: proto.Float64(1),
@@ -291,10 +283,6 @@ func testHandler(t tester) {
 						Name:  proto.String("basename"),
 						Value: proto.String("basevalue"),
 					},
-					&dto.LabelPair{
-						Name:  proto.String("__name__"),
-						Value: proto.String("name"),
-					},
 				},
 				Counter: &dto.Counter{
 					Value: proto.Float64(1),