Make extra sure that _getMainClosure is set to the correct value.

pkg/front_end/lib/src/fasta/kernel/kernel_target.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.
 
 library fasta.kernel_target;
 
 import 'dart:async' show
     Future;
 
 import 'dart:io' show
@@ skipping 211 matching lines @@
       if (astKind == AstKind.Analyzer) {
         loader.buildElementStore();
       } else {
         loader.computeHierarchy(program);
       }
       await loader.buildBodies(astKind);
       loader.finishStaticInvocations();
       finishAllConstructors();
       loader.finishNativeMethods();
       transformMixinApplications();
+      // TODO(ahe): Don't call this from two different places.
+      setup_builtin_library.transformProgram(program);
       errors.addAll(loader.collectCompileTimeErrors().map((e) => e.format()));
       if (errors.isNotEmpty) {
         return handleInputError(uri, null, isFullProgram: true);
       }
       if (uri == null) return program;
       return await writeLinkedProgram(uri, program, isFullProgram: true);
     } on InputError catch (e) {
       return handleInputError(uri, e, isFullProgram: true);
     } catch (e, s) {
       return reportCrash(e, s, loader?.currentUriForCrashReporting);
@@ skipping 337 matching lines @@
     superclass = superclass.superclass;
   }
   for (Constructor constructor in superclass.constructors) {
     if (constructor.name.name.isEmpty) {
       return constructor.function.requiredParameterCount == 0 ?
           constructor : null;
     }
   }
   return null;
 }