Implement new interfaces for noop types

noop.go

@@ -1,6 +1,10 @@
 package opentracing
 
-import "github.com/opentracing/opentracing-go/log"
+import (
+	"context"
+
+	"github.com/opentracing/opentracing-go/log"
+)
 
 // A NoopTracer is a trivial, minimum overhead implementation of Tracer
 // for which all operations are no-ops.
@@ -48,11 +52,19 @@ func (n noopSpan) LogEvent(event string)                                 {}
 func (n noopSpan) LogEventWithPayload(event string, payload interface{}) {}
 func (n noopSpan) Log(data LogData)                                      {}
 
+// noopSpan as SpanExt1
+func (n noopSpan) TracerExt1() TracerExt1 { return defaultNoopTracer }
+
 // StartSpan belongs to the Tracer interface.
 func (n NoopTracer) StartSpan(operationName string, opts ...StartSpanOption) Span {
 	return defaultNoopSpan
 }
 
+// StartSpanWithContext belongs to the TracerExt1 interface.
+func (n NoopTracer) StartSpanWithContext(ctx context.Context, operationName string, opts ...StartSpanOption) (context.Context, SpanExt1) {
+	return ContextWithSpan(ctx, defaultNoopSpan), defaultNoopSpan
+}
+
 // Inject belongs to the Tracer interface.
 func (n NoopTracer) Inject(sp SpanContext, format interface{}, carrier interface{}) error {
 	return nil