re-land fix #27110 with proper DDC side of changes

pkg/analyzer/lib/src/error/codes.dart

 // Copyright (c) 2014, 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 analyzer.src.error.codes;
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 
 /**
@@ skipping 4650 matching lines @@
       ", or enable implicit-dynamic in your Analyzer options.";
 
   static const String _inferredTypeMessage = '{0} has inferred type {1}';
 
   static const StrongModeCode DOWN_CAST_COMPOSITE = const StrongModeCode(
       ErrorType.STATIC_WARNING, 'DOWN_CAST_COMPOSITE', _implicitCastMessage);
 
   static const StrongModeCode DOWN_CAST_IMPLICIT = const StrongModeCode(
       ErrorType.HINT, 'DOWN_CAST_IMPLICIT', _implicitCastMessage);
 
+  static const StrongModeCode DOWN_CAST_IMPLICIT_ASSIGN = const StrongModeCode(
+      ErrorType.HINT, 'DOWN_CAST_IMPLICIT_ASSIGN', _implicitCastMessage);
+
   static const StrongModeCode DYNAMIC_CAST = const StrongModeCode(
       ErrorType.HINT, 'DYNAMIC_CAST', _implicitCastMessage);
 
   static const StrongModeCode ASSIGNMENT_CAST = const StrongModeCode(
       ErrorType.HINT, 'ASSIGNMENT_CAST', _implicitCastMessage);
 
   static const StrongModeCode INVALID_PARAMETER_DECLARATION =
       const StrongModeCode(ErrorType.COMPILE_TIME_ERROR,
           'INVALID_PARAMETER_DECLARATION', _typeCheckMessage);
 
@@ skipping 168 matching lines @@
    * Initialize a newly created error code to have the given [name].
    */
   const TodoCode(String name) : super(name, "{0}");
 
   @override
   ErrorSeverity get errorSeverity => ErrorSeverity.INFO;
 
   @override
   ErrorType get type => ErrorType.TODO;
 }