fix #27134, future unions in downwards generic method inference

pkg/analyzer/test/src/task/strong/inferred_type_test.dart

Index: pkg/analyzer/test/src/task/strong/inferred_type_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/inferred_type_test.dart b/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
index 5405293e7a4473e9f769d8ad82d86d9e2959f9f0..8b00a44b72d537704702e1fb310a9c377c954d5f 100644
--- a/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
+++ b/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
@@ -1676,6 +1676,24 @@ $downwards<int> g3(bool x) async {
     checkFile(build(downwards: "Future", upwards: "MyFuture"));
   }
 
+  void test_futureUnion_downwardsGenericMethods() {
+    // Regression test for https://github.com/dart-lang/sdk/issues/27134
+    //
+    // We need to take a future union into account for both directions of
+    // generic method inference.
+    checkFile(r'''
+import 'dart:async';
+
+foo() async {
+  Future<List<A>> f1 = null;
+  Future<List<A>> f2 = null;
+  List<List<A>> merged = await Future.wait(/*info:INFERRED_TYPE_LITERAL*/[f1, f2]);
+}
+
+class A {}
+    ''');
+  }
+
   void test_futureUnion_downwards() {
     String build({String declared, String downwards, String upwards}) {
       // TODO(leafp): The use of matchTypes in visitInstanceCreationExpression