provide MISSING_RETURN on factory constructors

pkg/analyzer/test/generated/non_error_resolver_test.dart

Index: pkg/analyzer/test/generated/non_error_resolver_test.dart
diff --git a/pkg/analyzer/test/generated/non_error_resolver_test.dart b/pkg/analyzer/test/generated/non_error_resolver_test.dart
index 28f721e735070c5eb6cf674b7810aa4264f2905e..e458070aaf457ab7e31cce97d784b3d1b720ae9c 100644
--- a/pkg/analyzer/test/generated/non_error_resolver_test.dart
+++ b/pkg/analyzer/test/generated/non_error_resolver_test.dart
@@ -2827,7 +2827,7 @@ f() {
   void test_invalidFactoryNameNotAClass() {
     Source source = addSource(r'''
 class A {
-  factory A() {}
+  factory A() => null;
 }''');
     computeLibrarySourceErrors(source);
     assertNoErrors(source);
@@ -3491,7 +3491,7 @@ class B extends Object with A {}''');
   void test_mixinDeclaresConstructor_factory() {
     Source source = addSource(r'''
 class A {
-  factory A() {}
+  factory A() => null;
 }
 class B extends Object with A {}''');
     computeLibrarySourceErrors(source);
@@ -4275,7 +4275,7 @@ class A {
     Source source = addSource(r'''
 class A {
   A.named() {}
-  factory A() {}
+  factory A() => null;
 }
 class B extends A {
   B() : super.named();
@@ -4693,7 +4693,7 @@ class B implements A {
   factory B() = C;
 }
 class C implements B {
-  factory C() {}
+  factory C() => null;
 }''');
     computeLibrarySourceErrors(source);
     assertNoErrors(source);