Add tests for is-checks on hidden native classes.

tests/language/src/NativeClassIsCheck2FrogTest.dart

+// Copyright (c) 2011, 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 for correct is-checks on hidden native classes.
+
+interface I {
+  I read();
+  write(I x);
+}
+
+// Native implementation.
+
+class A implements I native "*A" {
+  // The native class accepts only other native instances.
+  A read() native;
+  write(A x) native;
+}
+
+makeA() native;
+
+void setup() native """
+// This code is all inside 'setup' and so not accesible from the global scope.
+function A(){}
+A.prototype.read = function() { return this._x; };
+A.prototype.write = function(x) { this._x = x; };
+""";
+
+// Dart implementation must coexist with native implementation.
+
+class B implements I {
+  B b;
+  B read() { return b; }
+  write(B x) { b = x; }
+}
+
+main() {
+  setup();
+
+  var a1 = makeA();
+  var a2 = makeA();
+  var b1 = new B();
+  var b2 = new B();
+  var ob = new Object();
+
+  Expect.isFalse(ob is I);
+  Expect.isFalse(ob is A);
+  Expect.isFalse(ob is B);
+
+  Expect.isTrue(b1 is I);
+  Expect.isTrue(b1 is B);
+  Expect.isFalse(b1 is A);
+
+  Expect.isTrue(a1 is I);
+  Expect.isTrue(a1 is A);
+  Expect.isFalse(a1 is B);
+
+  new TypeParameterTest<B>(b1, b2);
+  new TypeParameterTest<I>(b1, b2);
+  new TypeParameterTest<A>(a1, a2);
+  new TypeParameterTest<I>(a1, a2);
+}
+
+class TypeParameterTest<T> {
+  T _x;
+  T _y;
+
+  TypeParameterTest(x, y) {
+    // In checked mode, the 'write' and 'read' operations will check arguments
+    // and results.
+    x.write(y);
+    y.write(x);
+    Expect.isTrue(x.read() === y);
+    Expect.isTrue(y.read() === x);
+
+    x.write(null);
+    y.write(null);
+    Expect.isTrue(x.read() === null);
+    Expect.isTrue(y.read() === null);
+
+    // Explicit checks against
+    var ob = new Object();
+    Expect.isTrue(ob is !T);
+    Expect.isTrue(x is T);
+    Expect.isTrue(y is T);
+
+    // In checked mode, there is a parameterized type assertion in assignment.
+    _x = x;
+    _y = y;
+  }
+}