anchor.diff:  
     @override
     void onQueueOpen(
  -      Enqueuer enqueuer, FunctionEntity mainMethod, Iterable<Uri> libraries) {
  +      Enqueuer enqueuer, FunctionEntity? mainMethod, Iterable<Uri> libraries) {
       enqueuer.applyImpact(_nativeEnqueuer.processNativeClasses(libraries));
       if (mainMethod != null) {
         enqueuer.applyImpact(_computeMainImpact(mainMethod));
  
positive.code:           .registerTypeUse(TypeUse.instantiation(_commonElements.typeType));
        // If the type is a web component, we need to ensure the constructors are
        // available to 'upgrade' the native object.
        if (constant.representedType is InterfaceType) {
          InterfaceType representedType = constant.representedType;
          _customElementsAnalysis.registerTypeConstant(representedType.element);
        }
      } else if (constant is InstantiationConstantValue) {
  
negative.code: // Copyright (c) 2017, 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.codegen_listener;
  
  