Allow string juxtapositions in exports.

sdk/lib/_internal/compiler/implementation/tree/nodes.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.
 
 part of tree;
 
 abstract class Visitor<R> {
   const Visitor();
 
   R visitNode(Node node);
@@ skipping 1720 matching lines @@
 /**
  * An [:export:] library tag.
  *
  * An export tag is dependency on another library where the exported identifiers
  * are put into the export scope of the exporting library. The export scope is
  * not visible inside the library.
  */
 class Export extends LibraryDependency {
   final Token exportKeyword;
 
-  Export(this.exportKeyword, LiteralString uri, NodeList combinators)
+  Export(this.exportKeyword, StringNode uri, NodeList combinators)
       : super(uri, combinators);
 
   bool get isExport => true;
 
   Export asExport() => this;
 
   accept(Visitor visitor) => visitor.visitExport(this);
 
   visitChildren(Visitor visitor) {
     uri.accept(visitor);
@@ skipping 246 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send != null) return f(send.arguments.head);
 }