Fix #28120, strong mode allows field overrides

pkg/analyzer/test/generated/compile_time_error_code_test.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.test.generated.compile_time_error_code_test;
 
 import 'dart:async';
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/error/codes.dart';
@@ skipping 5273 matching lines @@
 
 class B {
   int _x;
 }
 ''');
     Source source = addSource('''
 import 'lib1.dart';
 class C extends Object with A, B {}
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, [
-      CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-      StrongModeCode.INVALID_FIELD_OVERRIDE
-    ]);
+    assertErrors(
+        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
     verify([source]);
   }
 
   test_privateCollisionInMixinApplication_mixinAndMixin_indirect() async {
     resetWith(options: new AnalysisOptionsImpl()..strongMode = true);
     addNamedSource(
         '/lib1.dart',
         '''
 class A {
   int _x;
@@ skipping 25 matching lines @@
 
 class B {
   int _x;
 }
 ''');
     Source source = addSource('''
 import 'lib1.dart';
 class C extends A with B {}
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, [
-      CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-      StrongModeCode.INVALID_FIELD_OVERRIDE
-    ]);
+    assertErrors(
+        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
     verify([source]);
   }
 
   test_privateCollisionInMixinApplication_superclassAndMixin_same() async {
     resetWith(options: new AnalysisOptionsImpl()..strongMode = true);
     addNamedSource(
         '/lib1.dart',
         '''
 class A {
   int _x;
 }
 
 class B {
   int _x;
 }
 ''');
     Source source = addSource('''
 import 'lib1.dart';
 class C extends A with A {}
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, [
-      CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-      StrongModeCode.INVALID_FIELD_OVERRIDE
-    ]);
+    assertErrors(
+        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
     verify([source]);
   }
 
   test_privateOptionalParameter() async {
     Source source = addSource("f({var _p}) {}");
     await computeAnalysisResult(source);
     assertErrors(source, [CompileTimeErrorCode.PRIVATE_OPTIONAL_PARAMETER]);
     verify([source]);
   }
 
@@ skipping 1216 matching lines @@
         source, [CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_OPERATOR]);
     verify([source]);
     reset();
   }
 
   Future<Null> _check_wrongNumberOfParametersForOperator1(String name) async {
     await _check_wrongNumberOfParametersForOperator(name, "");
     await _check_wrongNumberOfParametersForOperator(name, "a, b");
   }
 }