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

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 1fae0c28064d6b14c983fe6895ed64e81e8acb97..4e4b890828a09d8d73cc4be11d1fa03cee885e6e 100644
--- a/pkg/analyzer/test/generated/non_error_resolver_test.dart
+++ b/pkg/analyzer/test/generated/non_error_resolver_test.dart
@@ -702,16 +702,6 @@ Future<Object> f() async {
     verify([source]);
   }
 
-  test_async_future_object_without_return() async {

[Brian Wilkerson, 2017/01/15 17:22:53]

We should test that we don't produce an error in cases where we shouldn't, such
as Future<Null>.

[scheglov, 2017/01/15 17:48:02]

There are tests:
test_async_future_null_with_return
test_async_future_null_without_return

-    Source source = addSource('''
-import 'dart:async';
-Future<Object> f() async {}
-''');
-    await computeAnalysisResult(source);
-    assertNoErrors(source);
-    verify([source]);
-  }
-
   test_async_future_with_return() async {
     Source source = addSource('''
 import 'dart:async';