Add 'tmpl', a 'template' for non-string literal names.

Change-Id: I6a03a5c5d20029cf414562efa7745ed6c53b2731

templates/templates.go

@@ -259,7 +259,15 @@ func (te templateExpander) ExpandHTML(templateFiles []string) (result string, re
 	}()
 
 	var buffer bytes.Buffer
-	tmpl, err := html_template.New(te.name).Funcs(html_template.FuncMap(te.funcMap)).Parse(te.text)
+	tmpl := html_template.New(te.name).Funcs(html_template.FuncMap(te.funcMap))
+        tmpl.Funcs(html_template.FuncMap{
+          "tmpl": func(name string, data interface{}) (html_template.HTML, error) {
+             var buffer bytes.Buffer
+             err := tmpl.ExecuteTemplate(&buffer, name, data)
+             return html_template.HTML(buffer.String()), err
+          },
+        })
+        tmpl, err := tmpl.Parse(te.text)
 	if err != nil {
 		return "", fmt.Errorf("Error parsing template %v: %v", te.name, err)
 	}

templates/templates_test.go

@@ -147,6 +147,12 @@ func TestTemplateExpansion(t *testing.T) {
 			text:   "{{ tableLink \"up\" }}",
 			output: "/graph#%5B%7B%22expr%22%3A%22up%22%2C%22tab%22%3A1%7D%5D",
 		},
+		{
+			// tmpl.
+			text:   "{{ define \"a\" }}x{{ end }}{{ $name := \"a\"}}{{ tmpl $name . }}",
+			output: "x",
+			html:   true,
+		},
 	}
 
 	time := clientmodel.Timestamp(0)