provide MISSING_RETURN on factory constructors

pkg/analyzer/test/generated/hint_code_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.hint_code_test;
 
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 1305 matching lines @@
     verify([source]);
   }
 
   void test_missingReturn_function() {
     Source source = addSource("int f() {}");
     computeLibrarySourceErrors(source);
     assertErrors(source, [HintCode.MISSING_RETURN]);
     verify([source]);
   }
 
+  void test_missingReturn_factory() {
+    Source source = addSource(r'''
+class A {
+  factory A() {}
+}
+''');
+    computeLibrarySourceErrors(source);
+    assertErrors(source, [HintCode.MISSING_RETURN]);
+    verify([source]);
+  }
+
   void test_missingReturn_method() {
     Source source = addSource(r'''
 class A {
   int m() {}
 }''');
     computeLibrarySourceErrors(source);
     assertErrors(source, [HintCode.MISSING_RETURN]);
     verify([source]);
   }
 
@@ skipping 1950 matching lines @@
   n() {
     var a = m(), b = m();
   }
 }''');
     computeLibrarySourceErrors(source);
     assertErrors(
         source, [HintCode.USE_OF_VOID_RESULT, HintCode.USE_OF_VOID_RESULT]);
     verify([source]);
   }
 }