Added support for exports and re-exports.

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.
 
 String unparse(Node node) {
   Unparser unparser = new Unparser();
   unparser.unparse(node);
   return unparser.result;
 }
 
@@ skipping 549 matching lines @@
   }
 
   visitExpression(Expression node) {
     throw 'internal error'; // Should not be called.
   }
 
   visitLibraryTag(LibraryTag node) {
     throw 'internal error'; // Should not be called.
   }
 
+  visitLibraryDependency(Node node) {
+    throw 'internal error'; // Should not be called.
+  }
+
   visitLiteral(Literal node) {
     throw 'internal error'; // Should not be called.
   }
 
   visitLoop(Loop node) {
     throw 'internal error'; // Should not be called.
   }
 
   visitPostfix(Postfix node) {
     throw 'internal error'; // Should not be called.
   }
 
   visitPrefix(Prefix node) {
     throw 'internal error'; // Should not be called.
   }
 
   visitStatement(Statement node) {
     throw 'internal error'; // Should not be called.
   }
 
   visitStringNode(StringNode node) {
     throw 'internal error'; // Should not be called.
   }
 }