Move AbstractFieldElement check into shouldOutput.

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 24 matching lines @@
      * Tells whether we should output given element. Corelib classes like
      * Object should not be in the resulting code.
      */
     final LIBS_TO_IGNORE = [
       compiler.jsHelperLibrary,
       compiler.interceptorsLibrary,
     ];
     bool shouldOutput(Element element) =>
       element.kind !== ElementKind.VOID &&
       LIBS_TO_IGNORE.indexOf(element.getLibrary()) == -1 &&
-      !isDartCoreLib(compiler, element.getLibrary());
+      !isDartCoreLib(compiler, element.getLibrary()) &&
+      element is !AbstractFieldElement;
 
     // TODO(smok): Refactor this traverse/collect mess.
     Set<TypedefElement> typedefs = new Set<TypedefElement>();
     Set<ClassElement> classes = new Set<ClassElement>();
     Set<Element> elements = new Set<Element>();
     Map<ClassElement, Set<Element>> resolvedClassMembers =
         new Map<ClassElement, Set<Element>>();
     PlaceholderCollector collector = new PlaceholderCollector(compiler);
     resolvedElements.forEach((element, treeElements) {
       if (!shouldOutput(element)) return;
       if (element.isMember()) {
         ClassElement enclosingClass = element.getEnclosingClass();
         assert(enclosingClass.isClass());
         assert(enclosingClass.isTopLevel());
         resolvedClassMembers
             .putIfAbsent(enclosingClass, () => new Set<Element>())
             .add(element);
         return;
       }
       if (!element.isTopLevel()) {
         compiler.cancel(reason: 'Cannot process $element', element: element);
       }
 
       elements.add(element);
     });
     resolvedElements.forEach((element, treeElements) {
       if (!shouldOutput(element)) return;
-      if (element is AbstractFieldElement) return;
       collector.collect(element, treeElements);
       new ReferencedElementCollector(
           compiler, element, treeElements, typedefs, classes)
       .collect();
     });
 
     final emptyTreeElements = new TreeElementMapping();
     collectElement(element) { collector.collect(element, emptyTreeElements); }
     typedefs.forEach(collectElement);
     classes.forEach(collectElement);
@@ skipping 87 matching lines @@
     }
     typeAnnotation.visitChildren(this);
   }
 
   void collect() {
     compiler.withCurrentElement(rootElement, () {
       rootElement.parseNode(compiler).accept(this);
     });
   }
 }