Revert "Minimal fix to get cross frame tests working."

lib/html/src/frog_DOMImplementation.dart

-// Copyright (c) 2012, 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.
-
-// TODO(vsm): Unify with Dartium version.
-class _DOMWindowCrossFrameImpl implements Window {
-  // Private window.
-  _WindowImpl _window;
-
-  // Fields.
-  // TODO(vsm): Implement history and location getters.
-
-  bool get closed() => _window.closed;
-  int get length() => _window.length;
-  Window get opener() => _createSafe(_window.opener);
-  Window get parent() => _createSafe(_window.parent);
-  Window get top() => _createSafe(_window.top);
-
-  // Methods.
-  void focus() => _window.focus();
-
-  void blur() => _window.blur();
-
-  void close() => _window.close();
-
-  void postMessage(Dynamic message,
-                   String targetOrigin,
-                   [List messagePorts = null]) {
-    if (messagePorts == null) {
-      _window.postMessage(message, targetOrigin);
-    } else {
-      _window.postMessage(message, targetOrigin, messagePorts);
-    }
-  }
-
-  // Implementation support.
-  _DOMWindowCrossFrameImpl(this._window);
-
-  static Window _createSafe(w) {
-    if (w === window) {
-      return w;
-    } else {
-      // TODO(vsm): Cache or implement equality.
-      return new _DOMWindowCrossFrameImpl(w);
-    }
-  }
-}