Add WorkItemBuilder to abstract WorkItem creation from the enqueuers.

pkg/compiler/lib/src/js_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.
 
 library js_backend.backend;
 
 import 'dart:async' show Future;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 
@@ skipping 1743 matching lines @@
   bool mayGenerateInstanceofCheck(DartType type) {
     // We can use an instanceof check for raw types that have no subclass that
     // is mixed-in or in an implements clause.
 
     if (!type.isRaw) return false;
     ClassElement classElement = type.element;
     if (isInterceptorClass(classElement)) return false;
     return _closedWorld.hasOnlySubclasses(classElement);
   }
 
-  WorldImpact registerUsedElement(Element element, {bool forResolution}) {
+  WorldImpact registerUsedElement(MemberElement element, {bool forResolution}) {
     WorldImpactBuilderImpl worldImpact = new WorldImpactBuilderImpl();
     if (element == helpers.disableTreeShakingMarker) {
       isTreeShakingDisabled = true;
     } else if (element == helpers.preserveNamesMarker) {
       mustPreserveNames = true;
     } else if (element == helpers.preserveMetadataMarker) {
       mustRetainMetadata = true;
     } else if (element == helpers.preserveUrisMarker) {
       if (compiler.options.preserveUris) mustPreserveUris = true;
     } else if (element == helpers.preserveLibraryNamesMarker) {
@@ skipping 357 matching lines @@
           }
         }
       }
     }
     // We also need top-level non-class elements like static functions and
     // global fields. We use the resolution queue to decide which elements are
     // part of the live world.
     for (LibraryElement lib in compiler.libraryLoader.libraries) {
       if (lib.isInternalLibrary) continue;
       lib.forEachLocalMember((Element member) {
-        if (!member.isClass &&
+        if (!(member.isClass || member.isTypedef) &&
             resolution.hasBeenProcessed(member) &&
             referencedFromMirrorSystem(member)) {
           reflectableMembers.add(member);
         }
       });
     }
     // And closures inside top-level elements that do not have a surrounding
     // class. These will be in the [:null:] bucket of the [closureMap].
     if (closureMap.containsKey(null)) {
       for (Element closure in closureMap[null]) {
@@ skipping 1116 matching lines @@
   @override
   bool isInterceptorClass(ClassElement cls) {
     return helpers.backend.isInterceptorClass(cls);
   }
 
   @override
   bool isNative(Element element) {
     return helpers.backend.isNative(element);
   }
 }