Improve test coverage for reflection on mixins.

tests/lib/mirrors/mixin_members_test.dart

+// Copyright (c) 2013, 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.
+
+import "dart:mirrors";
+
+import "package:expect/expect.dart";
+
+class Fooer {
+  foo1();
+}
+
+class S implements Fooer {
+  foo1() {}
+  foo2() {}
+}
+
+class M1 {
+  bar1() {}
+  bar2() {}
+}
+
+class M2 {
+  baz1() {}
+  baz2() {}
+}
+
+class C extends S with M1, M2 {}
+
+main() {
+  ClassMirror cm = reflectClass(C);
+  Classmirror sM1M2 = cm.superclass;
+  Classmirror sM1 = sM1M2.superclass;
+  ClassMirror s = sM1.superclass;
+  Expect.equals(0, cm.members.length);
+  Expect.setEquals(sM1M2.members.keys,
+                   [const Symbol("baz1"), const Symbol("baz2")]);
+  Expect.setEquals(sM1M2.superinterfaces.map((e) => e.simpleName),
+                   [const Symbol("M2")]);
+  Expect.setEquals(sM1.members.keys,
+                   [const Symbol("bar1"), const Symbol("bar2")]);
+  Expect.setEquals(sM1.superinterfaces.map((e) => e.simpleName),
+                   [const Symbol("M1")]);
+  Expect.setEquals(s.members.keys.toSet(),
+                   [const Symbol("foo1"), const Symbol("foo2")]);
+  Expect.setEquals(s.superinterfaces.map((e) => e.simpleName),
+                   [const Symbol("Fooer")]);
+  Expect.equals(true, reflectClass(S) == s);
+}