Import rasta tests.

pkg/fasta/test/rasta/mixin_library.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.md file.
+
+library test.mixin_library;
+
+f() => 2;
+
+V() => 87;
+
+_private() => 117;
+
+class Mixin<T> {
+  var x = f(), y, z;
+  T t;
+  foo() => super.foo() + f();
+  T g(T a) => null;
+  h() => V();
+  l() => _private();
+  _privateMethod() => 49;
+  publicMethod() => _privateMethod();
+}
+
+foo(m) => m._privateMethod();