Opportunistically call Init() from WrapHandler

tracing/tracing.go

@@ -148,6 +148,8 @@ func Init() {
 
 // WrapTransport optionally wraps a http.RoundTripper with OpenCensus
 // tracing functionality, if it is globally enabled.
+//
+// Must call Init() first.
 func WrapTransport(t http.RoundTripper) http.RoundTripper {
 	if Enabled {
 		t = othttp.NewTransport(t)
@@ -158,10 +160,10 @@ func WrapTransport(t http.RoundTripper) http.RoundTripper {
 // WrapHandler wraps a http.Handler with OpenCensus tracing
 // functionality, if globally enabled. Automatically calls Init().
 func WrapHandler(h http.Handler, endpointAddr string) http.Handler {
-	if Enabled {
 	serviceName := getServiceName()
 	initTracing(serviceName)
-		h = othttp.NewHandler(h, serviceName)
-	}
+	if !Enabled {
 		return h
 	}
+	return othttp.NewHandler(h, serviceName)
+}