Allow values to be returned from implicitly typed setters

pkg/analyzer/test/generated/strong_mode_test.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 analyzer.test.generated.strong_mode_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
@@ skipping 1951 matching lines @@
 class A {
   set f(String s) {
     return '42';
   }
 }
 set g(int x) => 42;
 ''');
     computeLibrarySourceErrors(source);
     assertErrors(source, [
       StaticTypeWarningCode.RETURN_OF_INVALID_TYPE,
-      StaticTypeWarningCode.RETURN_OF_INVALID_TYPE
     ]);
     verify([source]);
   }
 
   void test_setterWithNoVoidType_returningVoid() {
     Source source = addSource(r'''
 void returnsVoid() {}
 class A {
   set f(String s) => returnsVoid();
 }
@@ skipping 288 matching lines @@
 main() {
   var v = x;
   v; // marker
 }
 int x = 3;
 ''';
     assertPropagatedAssignedType(code, typeProvider.intType, null);
     assertTypeOfMarkedExpression(code, typeProvider.intType, null);
   }
 }