dart2dart properly collect top level fields

lib/compiler/implementation/dart_backend/placeholder_collector.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 LocalPlaceholder implements Hashable {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
   int hashCode() => identifier.hashCode();
   String toString() =>
@@ skipping 157 matching lines @@
       for (Node definition in node.definitions) {
         if (definition is Identifier) {
           tryMakePrivateIdentifier(definition.asIdentifier());
         } else if (definition is SendSet) {
           tryMakePrivateIdentifier(
               definition.asSendSet().selector.asIdentifier());
         } else {
           internalError('Unreachable case');
         }
       }
+    } else if (element.isTopLevel()) {
+      Node fieldNode = element.parseNode(compiler);
+      if (fieldNode is Identifier) {
+        makeElementPlaceholder(fieldNode, element);
+      } else if (fieldNode is SendSet) {
+        makeElementPlaceholder(fieldNode.selector, element);
+      } else {
+        internalError('Unreachable case');
+      }
     }
   }
   
   void collect(Element element, TreeElements elements) {
     treeElements = elements;
     Node elementNode;
     if (element is FunctionElement) {
       currentElement = element;
       elementNode = currentElement.parseNode(compiler);
       collectFunctionDeclarationPlaceholders(element, elementNode);
     } else if (element.isField()) {
       // TODO(smok): In the future make sure we don't process same
       // variable list element twice, better merge this with emitter logic.
       currentElement = (element as VariableElement).variables;
       elementNode = currentElement.parseNode(compiler);
+      // We don't collect other elements from the same variable lists
+      // if they are not used. http://dartbug.com/4536
       collectFieldDeclarationPlaceholders(element, elementNode);
     } else if (element is ClassElement || element is TypedefElement) {
       currentElement = element;
       elementNode = currentElement.parseNode(compiler);
     } else {
       assert(false); // Unreachable.
     }
     currentLocalPlaceholders = new Map<String, LocalPlaceholder>();
     compiler.withCurrentElement(element, () {
       elementNode.accept(this);
@@ skipping 202 matching lines @@
     makeElementPlaceholder(node.name, currentElement);
     node.visitChildren(this);
   }
 
   visitTypedef(Typedef node) {
     assert(currentElement is TypedefElement);
     makeElementPlaceholder(node.name, currentElement);
     node.visitChildren(this);
   }
 }