Add FunctionDeclaration node.

frog/leg/tree/unparser.dart

Index: frog/leg/tree/unparser.dart
diff --git a/frog/leg/tree/unparser.dart b/frog/leg/tree/unparser.dart
index e5ffc7ffa319011fdeee3be6ccd52db0d0e90abf..6c87aef22e94af3ec69739afe5266efe61ac1989 100644
--- a/frog/leg/tree/unparser.dart
+++ b/frog/leg/tree/unparser.dart
@@ -75,6 +75,10 @@ class Unparser implements Visitor {
     visit(node.body);
   }
 
+  visitFunctionDeclaration(FunctionDeclaration node) {
+    visit(node.function);
+  }
+
   visitFunctionExpression(FunctionExpression node) {
     if (node.returnType !== null) {
       visit(node.returnType);