Add strong mode error for mixins defining conflicting private names (issue 28809)

pkg/analyzer/lib/error/error.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.error.error;
 
 import 'dart:collection';
 
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/scanner/scanner.dart' show ScannerErrorCode;
@@ skipping 175 matching lines @@
   CompileTimeErrorCode.NON_GENERATIVE_CONSTRUCTOR,
   CompileTimeErrorCode.NOT_ENOUGH_REQUIRED_ARGUMENTS,
   CompileTimeErrorCode.NO_ANNOTATION_CONSTRUCTOR_ARGUMENTS,
   CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_EXPLICIT,
   CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_IMPLICIT,
   CompileTimeErrorCode.OBJECT_CANNOT_EXTEND_ANOTHER_CLASS,
   CompileTimeErrorCode.OPTIONAL_PARAMETER_IN_OPERATOR,
   CompileTimeErrorCode.PART_OF_NON_PART,
   CompileTimeErrorCode.PREFIX_COLLIDES_WITH_TOP_LEVEL_MEMBER,
   CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
+  CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
   CompileTimeErrorCode.PRIVATE_OPTIONAL_PARAMETER,
   CompileTimeErrorCode.RECURSIVE_COMPILE_TIME_CONSTANT,
   CompileTimeErrorCode.RECURSIVE_CONSTRUCTOR_REDIRECT,
   CompileTimeErrorCode.RECURSIVE_FACTORY_REDIRECT,
   CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE,
   CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_EXTENDS,
   CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_IMPLEMENTS,
   CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_WITH,
   CompileTimeErrorCode.REDIRECT_GENERATIVE_TO_MISSING_CONSTRUCTOR,
   CompileTimeErrorCode.REDIRECT_GENERATIVE_TO_NON_GENERATIVE_CONSTRUCTOR,
@@ skipping 620 matching lines @@
    * a single list of errors.
    */
   static List<AnalysisError> mergeLists(List<List<AnalysisError>> errorLists) {
     Set<AnalysisError> errors = new HashSet<AnalysisError>();
     for (List<AnalysisError> errorList in errorLists) {
       errors.addAll(errorList);
     }
     return errors.toList();
   }
 }