Better mirrors support for mixins and private fields

pkg/dev_compiler/test/codegen/lib/mirrors/mixin_simple_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.
+
+library test.mixin;
+
+import 'dart:mirrors';
+
+import 'package:expect/expect.dart';
+
+class Super {}
+class Mixin {}
+class Mixin2 {}
+
+class Class extends Super with Mixin {}
+class MultipleMixins extends Class with Mixin2 {}
+
+main() {
+  Expect.equals(reflectClass(Class),
+                reflectClass(Class).mixin);
+  Expect.equals(reflectClass(Mixin),
+                reflectClass(Class).superclass.mixin);
+  Expect.equals(reflectClass(Super),
+                reflectClass(Class).superclass.superclass.mixin);
+
+  Expect.equals(reflectClass(MultipleMixins),
+                reflectClass(MultipleMixins).mixin);
+  Expect.equals(reflectClass(Mixin2),
+                reflectClass(MultipleMixins).superclass.mixin);
+  Expect.equals(reflectClass(Class),
+                reflectClass(MultipleMixins).superclass.superclass.mixin);
+  Expect.equals(reflectClass(Mixin),
+                reflectClass(MultipleMixins).superclass.superclass.superclass
+                    .mixin);
+  Expect.equals(reflectClass(Super),
+                reflectClass(MultipleMixins).superclass.superclass.superclass
+                    .superclass.mixin);
+}