Make string juxtaposition combine properly with string interpolations.

frog/leg/resolver.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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
 }
 
 class TreeElementMapping implements TreeElements {
@@ skipping 885 matching lines @@
 
   visitLiteralBool(LiteralBool node) {
   }
 
   visitLiteralString(LiteralString node) {
   }
 
   visitLiteralNull(LiteralNull node) {
   }
 
+  visitStringJuxtaposition(StringJuxtaposition node) {
+    if (node.isInterpolation) node.visitChildren(this);
+  }
+
   visitNodeList(NodeList node) {
     for (Link<Node> link = node.nodes; !link.isEmpty(); link = link.tail) {
       visit(link.head);
     }
   }
 
   visitOperator(Operator node) {
     unimplemented(node, 'operator');
   }
 
@@ skipping 740 matching lines @@
 class TopScope extends Scope {
   LibraryElement get library() => element;
 
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) => library.find(name);
 
   Element add(Element element) {
     throw "Cannot add an element in the top scope";
   }
 }