dart2dart Fix collecting type of class fields

lib/compiler/implementation/dart_backend/backend.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 DartBackend extends Backend {
   final List<CompilerTask> tasks;
   final UnparseValidator unparseValidator;
 
   Map<Element, TreeElements> get resolvedElements() =>
       compiler.enqueuer.resolution.resolvedElements;
@@ skipping 127 matching lines @@
  */
 class ReferencedElementCollector extends AbstractVisitor {
   final Compiler compiler;
   final Element rootElement;
   final TreeElements treeElements;
   final newTypedefElementCallback;
   final newClassElementCallback;
 
   ReferencedElementCollector(
       this.compiler,
-      this.rootElement, this.treeElements,
-      this.newTypedefElementCallback, this.newClassElementCallback);
+      Element rootElement, this.treeElements,
+      this.newTypedefElementCallback, this.newClassElementCallback)
+      : this.rootElement = (rootElement is VariableElement)
+          ? (rootElement as VariableElement).variables : rootElement;
 
   visitClassNode(ClassNode node) {
     super.visitClassNode(node);
     // Temporary hack which should go away once interfaces
     // and default clauses are out.
     if (node.defaultClause !== null) {
       // Resolver cannot resolve parameterized default clauses.
       TypeAnnotation evilCousine = new TypeAnnotation(
           node.defaultClause.typeName, null);
       evilCousine.accept(this);
     }
   }
 
   visitNode(Node node) { node.visitChildren(this); }
 
   visitTypeAnnotation(TypeAnnotation typeAnnotation) {
     final type = compiler.resolveTypeAnnotation(rootElement, typeAnnotation);
     Element typeElement = type.element;
     if (typeElement.isTypedef()) newTypedefElementCallback(typeElement);
     if (typeElement.isClass()) newClassElementCallback(typeElement);
     typeAnnotation.visitChildren(this);
   }
 
   void collect() {
     compiler.withCurrentElement(rootElement, () {
       rootElement.parseNode(compiler).accept(this);
     });
   }
 }