Remove proxying support from dart:html

tests/html/js_interop_element_test.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
-
-#library('JsInteropElementTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
-#import('dart:isolate');
-
-injectSource(code) {
-  final script = new ScriptElement();
-  script.type = 'text/javascript';
-  script.innerHTML = code;
-  document.body.nodes.add(script);
-}
-
-var jsElementTest = """
-  var canvas = document.createElement('canvas');
-  document.body.appendChild(canvas);
-
-  var port = window.lookupPort('test1');
-  port.callSync(canvas);
-""";
-
-var dartElementTest = """
-  var port = new ReceivePortSync();
-  port.receive(function (data) {
-    return (data instanceof HTMLDivElement);
-  });
-  window.registerPort('test2', port.toSendPort());
-""";
-
-main() {
-  useHtmlConfiguration();
-
-  test('js-element', () {
-    int invoked = 0;
-
-    var port = new ReceivePortSync();
-    port.receive((data) {
-      expect(data is CanvasElement);
-      ++invoked;
-    });
-    window.registerPort('test1', port.toSendPort());
-
-    injectSource(jsElementTest);
-    expect(invoked, equals(1));
-  });
-
-  test('dart-element', () {
-    injectSource(dartElementTest);
-
-    var port = window.lookupPort('test2');
-    var div = new DivElement();
-    var canvas = new CanvasElement(100,100);
-    document.body.nodes.addAll([div, canvas]);
-    expect(port.callSync(div));
-    expect(!port.callSync(canvas));
-  });
-}