Added support for exports and re-exports.

lib/compiler/implementation/dart_backend/utils.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 CloningVisitor implements Visitor<Node> {
   final TreeElements originalTreeElements;
   final TreeElementMapping cloneTreeElements;
 
   CloningVisitor(this.originalTreeElements)
       : cloneTreeElements = new TreeElementMapping();
@@ skipping 214 matching lines @@
   }
 
   Node visitGotoStatement(GotoStatement node) {
     unimplemented('visitNode', node: node);
   }
 
   Node visitImport(Import node) {
     unimplemented('visitNode', node: node);
   }
 
+  Node visitLibraryDependency(LibraryTag node) {
+    unimplemented('visitNode', node: node);
+  }
+
   Node visitLibraryName(LibraryName node) {
     unimplemented('visitNode', node: node);
   }
 
   Node visitLibraryTag(LibraryTag node) {
     unimplemented('visitNode', node: node);
   }
 
   Node visitLiteral(Literal node) {
     unimplemented('visitNode', node: node);
@@ skipping 24 matching lines @@
   }
 
   Node visitStringNode(StringNode node) {
     unimplemented('visitNode', node: node);
   }
 
   unimplemented(String message, {Node node}) {
     throw message;
   }
 }