Copy lib/dom tests that use dart:html to lib/html.

tests/dom/hidden_dom_1_test.dart

-#library('HiddenDom1Test');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
-#import('dart:html');
-
-// Test that the dart:html API does not leak native jsdom methods:
-//   onfocus setter.
-
-main() {
-  useHtmlConfiguration();
-
-  test('test1', () {
-    document.body.elements.add(new Element.html(@'''
-<div id='div1'>
-Hello World!
-</div>'''));
-    Element e = document.query('#div1');
-    Expect.isTrue(e != null);
-
-    checkNoSuchMethod(() { confuse(e).onfocus = null; });
-  });
-
-}
-
-class Decoy {
-  void set onfocus(x) { throw 'dead code'; }
-}
-
-confuse(x) => opaqueTrue() ? x : (opaqueTrue() ? new Object() : new Decoy());
-
-/** Returns [:true:], but in a way that confuses the compiler. */
-opaqueTrue() => true;  // Expand as needed.
-
-checkNoSuchMethod(action()) {
-  var ex = null;
-  try {
-    action();
-  } catch (var e) {
-    ex = e;
-  }
-  if (ex === null)
-    Expect.fail('Action should have thrown exception');
-
-  Expect.isTrue(ex is NoSuchMethodException, 'ex is NoSuchMethodException');
-}