Report HintCode.MISSING_RETURN for async functions with return type that matters.

pkg/analyzer/test/generated/hint_code_test.dart

Index: pkg/analyzer/test/generated/hint_code_test.dart
diff --git a/pkg/analyzer/test/generated/hint_code_test.dart b/pkg/analyzer/test/generated/hint_code_test.dart
index 52b0febf25bf92c570fbce05e5e66a5dc5004015..07096ce70c973641298e86db84e2566f1924c2f1 100644
--- a/pkg/analyzer/test/generated/hint_code_test.dart
+++ b/pkg/analyzer/test/generated/hint_code_test.dart
@@ -168,6 +168,16 @@ n(int i) {}''');
     verify([source]);
   }
 
+  test_async_future_object_without_return() async {
+    Source source = addSource('''
+import 'dart:async';
+Future<Object> f() async {}
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source, [HintCode.MISSING_RETURN]);
+    verify([source]);
+  }
+
   test_canBeNullAfterNullAware_false_methodInvocation() async {
     Source source = addSource(r'''
 m(x) {