fix #27382, tweak inference heuristic when we have no upper bound info

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

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 /// Tests for type inference.
 library analyzer.test.src.task.strong.inferred_type_test;
 
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 1749 matching lines @@
   List<A> list = result;
   list = result2;
 }
 
 class A {}
 class B extends A {}
 class C extends A {}
     ''');
   }
 
+  void test_genericFunctions_returnTypedef() {
+    checkFile(r'''
+typedef void ToValue<T>(T value);
+
+main() {
+  ToValue/*<T>*/ f/*<T>*/(dynamic /*=T*/ x) => null;
+  var x = f/*<int>*/(42);
+  var y = f(42);
+  ToValue<int> takesInt = x;
+  takesInt = y;
+}
+    ''');
+  }
+
   void test_genericMethods_basicDownwardInference() {
     checkFile(r'''
 /*=T*/ f/*<S, T>*/(/*=S*/ s) => null;
 main() {
   String x = f(42);
   String y = (f)(42);
 }
 ''');
   }
 
@@ skipping 2774 matching lines @@
   }
 
   /// Adds a file using [helper.addFile] and calls [helper.check].
   ///
   /// Also returns the resolved compilation unit.
   @override
   CompilationUnitElement checkFile(String content) {
     return helper.checkFile(content).element;
   }
 }