Allow native classes to mixin behavior from an ordinary Dart class.

tests/compiler/dart2js_native/native_mixin_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.
+
+// Test that native classes can use ordinary Dart classes as mixins.
+
+class A native "*A" {
+  foo() => 42;
+  baz() => 99;
+}
+
+class B extends A with M native "*B" {
+  bar() => baz();
+}
+
+class M {
+  foo() => 87;
+  bar() => 101;
+}
+
+A makeA() native;
+B makeB() native;
+
+void setup() native """
+function A() {}
+function B() {}
+makeA = function(){return new A;};
+makeB = function(){return new B;};
+""";
+
+main() {
+  setup();
+  A a = makeA();
+  Expect.equals(42, a.foo());
+  Expect.throws(() => a.bar(), (error) => error is NoSuchMethodError);
+  Expect.equals(99, a.baz());
+  Expect.isTrue(a is A);
+  Expect.isFalse(a is B);
+  Expect.isFalse(a is M);
+
+  B b = makeB();
+  Expect.equals(87, b.foo());
+  Expect.equals(99, b.bar());
+  Expect.equals(99, b.baz());
+  Expect.isTrue(b is A);
+  Expect.isTrue(b is B);
+  Expect.isTrue(b is M);
+
+  M m = new M();
+  Expect.equals(87, m.foo());
+  Expect.equals(101, m.bar());
+  Expect.throws(() => m.baz(), (error) => error is NoSuchMethodError);
+  Expect.isFalse(m is A);
+  Expect.isFalse(m is B);
+  Expect.isTrue(m is M);
+}