Handle private fields from mixins.

tests/language/private_other_mixin2.lib

Index: tests/language/private_other_mixin2.lib
diff --git a/samples/tests/samples/standalone/time_test.dart b/tests/language/private_other_mixin2.lib
similarity index 54%
copy from samples/tests/samples/standalone/time_test.dart
copy to tests/language/private_other_mixin2.lib
index 32a8726ccaba707e59d14c9eb5589b446682c6d3..c23e7b5dfe31fa99ef027d93a6ee669d965d0ead 100644
--- a/samples/tests/samples/standalone/time_test.dart
+++ b/tests/language/private_other_mixin2.lib
@@ -2,13 +2,14 @@
 // 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.
 
-import '../../../time/time_server.dart' as time;
+// Dart test for testing access to private fields on mixins.
 
-// @static-clean
-
-/**
- * This test exists to ensure that the time sample compiles without errors.
- */
-void main() {
+library private_mixin2_other;
 
+class C1 {
+  int _field = 42;
 }
+
+class C2 extends Object with C1 {
+  int get field => _field;
+}