Resolve signature from correct scope class (fix #25609).

tests/language/regress_25609_test.dart

 // Copyright (c) 2016, 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.
 
-void f() {
-  f_called = true;
+// VMOptions=--error-on-bad-type
+
+import 'regress_25609_lib1.dart';
+
+Foo baz() => null;
+
+main () {
+  baz();
 }
-
-bool f_called = false;