Set Content-Type on static files.

Fixes google#763

pages/static/static.go

@@ -18,8 +18,10 @@ package static
 
 import (
 	"fmt"
+	"mime"
 	"net/http"
 	"net/url"
+	"path"
 )
 
 const StaticResource = "/static/"
@@ -46,6 +48,12 @@ func HandleRequest(w http.ResponseWriter, u *url.URL) error {
 		return fmt.Errorf("unknown static resource %q", resource)
 	}
 
+	// Set Content-Type if we were able to detect it.
+	contentType := mime.TypeByExtension(path.Ext(resource))
+	if contentType != "" {
+		w.Header().Set("Content-Type", contentType)
+	}
+
 	_, err := w.Write([]byte(content))
 	return err
 }