Create ResolutionEnqueuer after library loading.

tests/compiler/dart2js/kernel/visitor_test.dart

 // Copyright (c) 2016, 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.
 
 /// Test that the dart2js copy of [KernelVisitor] generates the expected IR as
 /// defined by kernel spec-mode test files.
 
 import 'dart:io';
 import 'dart:async';
 import 'package:compiler/src/compiler.dart' show Compiler;
@@ skipping 62 matching lines @@
 
 Future<Compiler> newCompiler() async {
   var compiler = compilerFor(
       options: [Flags.analyzeOnly, Flags.analyzeAll, Flags.useKernel]);
   await compiler.setupSdk();
 
   // The visitor no longer enqueues elements that are not reachable from the
   // program. The mixin-full resolution transform run by the test expects to
   // find dart.core::Iterator.
   var core = await compiler.libraryLoader.loadLibrary(Uri.parse('dart:core'));
+  compiler.startResolution();
   var cls = core.implementation.localLookup('Iterator');
   cls.ensureResolved(compiler.resolution);
   return compiler;
 }