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

test/codegen/lib/html/dom_constructors_test.dart

+library DOMConstructorsTest;
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+import 'dart:html';
+
+main() {
+  useHtmlConfiguration();
+  test('FileReader', () {
+    FileReader fileReader = new FileReader();
+    expect(fileReader.readyState, equals(FileReader.EMPTY));
+  });
+}