Add test for Frog native class with same native name as interface.

tests/language/src/NativeLibrarySameNameUsedFrogTest.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 hidden native class when interface has same name.
+
+#import('NativeLibrarySameNameUsedLib1.dart');
+
+void setup() native """
+  // This code is all inside 'setup' and so not accesible from the global scope.
+  function I(){}
+  I.prototype.read = function() { return this._x; };
+  I.prototype.write = function(x) { this._x = x; };
+  makeI = function(){return new I};
+""";
+
+// A pure Dart implementation of I.
+
+class ProxyI implements I {
+  ProxyI b;
+  ProxyI read() { return b; }
+  write(ProxyI x) { b = x; }
+}
+
+main() {
+  setup();
+
+  var a1 = makeI();
+  var a2 = makeI();
+  var b1 = new ProxyI();
+  var b2 = new ProxyI();
+  var ob = new Object();
+
+  Expect.isFalse(ob is I,      'ob is I');
+  Expect.isFalse(ob is ProxyI, 'ob is ProxyI');
+
+  Expect.isTrue(b1 is I,       'b1 is I');
+  Expect.isTrue(b1 is ProxyI,  'b1 is ProxyI');
+
+  Expect.isTrue(a1 is I,       'a1 is I');
+  Expect.isFalse(a1 is ProxyI, 'a1 is ProxyI');
+}