dart2dart: Introduce Renamer that is used by renaming unparser

lib/compiler/implementation/tree/unparser.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class Unparser implements Visitor {
   StringBuffer sb;
 
   Unparser();
 
   String unparse(Node node) {
@@ skipping 165 matching lines @@
     sb.add(' ');
     visit(node.elements);
   }
 
   visitModifiers(Modifiers node) => node.visitChildren(this);
 
   /**
    * Unparses given NodeList starting from specific node.
    */
   unparseNodeListFrom(NodeList node, Link<Node> from) {
+    if (from.isEmpty()) return;
     String delimiter = (node.delimiter === null) ? " " : "${node.delimiter} ";
-    from.printOn(sb, delimiter);
+    visit(from.head);
+    for (Link link = from.tail; !link.isEmpty(); link = link.tail) {
+      sb.add(delimiter);
+      visit(link.head);
+    }
   }
 
   visitNodeList(NodeList node) {
     if (node.beginToken !== null) add(node.beginToken.value);
     if (node.nodes !== null) {
       unparseNodeListFrom(node, node.nodes);
     }
     if (node.endToken !== null) add(node.endToken.value);
   }
 
@@ skipping 274 matching lines @@
       sb.add(' ');
     }
     visit(node.name);
     if (node.typeParameters !== null) {
       visit(node.typeParameters);
     }
     visit(node.formals);
     add(node.endToken.value);
   }
 }