Further encapsulate Enqueuer

tests/compiler/dart2js/embedded_category_api_boundary_test.dart

 // Copyright (c) 2015, the Fletch 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.md file.
 
 /// Tests that analyzing everything from the libraries that are public from the
 /// embedded category does not cause elements from other libraries to be
 /// processed.
 library embedded_category_boundary_test;
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:sdk_library_metadata/libraries.dart';
 
 import 'analyze_helper.dart';
 
 main() async {
   List<Uri> uriList = new List<Uri>();
   libraries.forEach((String name, LibraryInfo info) {
     if (info.categories.contains(Category.embedded)) {
       uriList.add(new Uri(scheme: 'dart', path: name));
     }
   });
   asyncTest(() async {
-    analyze(uriList, {}, checkResults: checkResults, mode: AnalysisMode.MAIN);
+    await analyze(uriList, {},
+        checkResults: checkResults, mode: AnalysisMode.MAIN);
   });
 }
 
 /// These elements are currently escaping from dart:async via
 /// `core._Resource#_readAsStream`.
 Set<String> whiteList = new Set.from([
   "function(StreamController#addError)",
   "getter(StreamController#stream)",
   "setter(StreamController#onListen)"
 ]);
 
 bool checkResults(Compiler compiler, CollectingDiagnosticHandler handler) {
   return compiler.enqueuer.resolution.processedElements
       .every((Element element) {
     if (whiteList.contains("$element")) return true;
     LibraryInfo info = libraries[element.library.canonicalUri.path];
     bool isAllowedInEmbedded =
         info.isInternal || info.categories.contains(Category.embedded);
+    if (!isAllowedInEmbedded) {
+      print(
+          'Disallowed element: $element from ${element.library.canonicalUri}');
+    }
     return isAllowedInEmbedded;
   });
 }