Fixed nits from Cody.

Change-Id: I037f7313217d75f29f7150c53c1cd28a0ec7ea35

google/internal/externalaccount/urlcredsource_test.go

@@ -7,6 +7,7 @@ package externalaccount
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -19,11 +20,18 @@ func TestRetrieveURLSubjectToken_Text(t *testing.T) {
 		if r.Method != "GET" {
 			t.Errorf("Unexpected request method, %v is found", r.Method)
 		}
+		fmt.Println(r.Header)
+		if r.Header.Get("Metadata") != "True" {
+			t.Errorf("Metadata header not properly included.")
+		}
 		w.Write([]byte("testTokenValue"))
 	}))
+	heads := make(map[string]string)
+	heads["Metadata"] = "True"
 	cs := CredentialSource{
 		URL:    ts.URL,
 		Format: format{Type: fileTypeText},
+		Headers: heads,
 	}
 	tfc := testFileConfig
 	tfc.CredentialSource = cs