Add all dart:html tests from the sdk to test/codegen.

test/codegen/lib/html/hidden_dom_1_test.dart

+library HiddenDom1Test;
+import 'package:unittest/unittest.dart';
+import 'package: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.children.add(new Element.html(r'''
+<div id='div1'>
+Hello World!
+</div>'''));
+    Element e = document.query('#div1');
+    expect(e, isNotNull);
+
+    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 (e) {
+    ex = e;
+  }
+  if (ex == null)
+    expect(false, isTrue, reason: 'Action should have thrown exception');
+
+  expect(ex, isNoSuchMethodError);
+}