Add WorkItemBuilder to abstract WorkItem creation from the enqueuers.

pkg/compiler/lib/src/compiler.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 dart2js.compiler_base;
 
 import 'dart:async' show EventSink, Future;
 
 import '../compiler_new.dart' as api;
 import 'cache_strategy.dart' show CacheStrategy;
@@ skipping 751 matching lines @@
     void registerStaticUse(Element element) {
       impactBuilder.registerStaticUse(new StaticUse.directUse(element));
     }
 
     void registerElement(Element element) {
       if (element.isClass) {
         ClassElement cls = element;
         cls.ensureResolved(resolution);
         cls.forEachLocalMember(registerStaticUse);
         impactBuilder.registerTypeUse(new TypeUse.instantiation(cls.rawType));
+      } else if (element.isTypedef) {

[Siggi Cherem (dart-lang), 2016/12/20 21:21:47]

I feel I missed something: why typedefs are now handled differently? I didn't
find the relation between that and adding the workitem builder abstration

[Johnni Winther, 2016/12/21 10:19:37]

Typedef should never have been added to the work-list. The work-item created for
them would effectively call `ensureResolved` as below. They were the last reason
why we couldn't state that all enqueued entities were MemberEntity; which is why
the change is in this CL.

+        TypedefElement typdef = element;
+        typdef.ensureResolved(resolution);
       } else {
         registerStaticUse(element);
       }
     }
 
     library.implementation.forEachLocalMember(registerElement);
 
     library.imports.forEach((ImportElement import) {
       if (import.isDeferred) {
         // `import.prefix` and `loadLibrary` may be `null` when the deferred
@@ skipping 1443 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }