Start cleaning up the HTML tests.

pkg/dev_compiler/test/codegen/lib/html/htmlelement_test.dart

-library ElementTest;
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
 import 'dart:html';
+
+import 'package:minitest/minitest.dart';
+
 import 'utils.dart';
 
 main() {
-  useHtmlConfiguration();
   test('InnerHTML', () {
     Element element = new Element.tag('div');
     element.id = 'test';
     element.innerHtml = 'Hello World';
     document.body.append(element);
 
     element = document.query('#test');
     expect(element.innerHtml, 'Hello World');
     element.remove();
   });
   test('HTMLTable', () {
-    Element table = new Element.tag('table');
+    TableElement table = new Element.tag('table');
 
     TableRowElement row = new Element.tag('tr');
     table.append(row);
 
     row.append(new Element.tag('td'));
     row.append(new Element.tag('td'));
 
     expect(row.cells.length, 2);
 
     TableRowElement headerRow = table.rows[0];
@@ skipping 62 matching lines @@
         '<div id="dataDiv" data-my-message="Hello World"></div>',
         treeSanitizer: new NullTreeSanitizer());
     expect(otherDiv.dataset.containsKey('myMessage'), isTrue);
 
     Element anotherDiv = new Element.html(
         '<div id="dataDiv" data-eggs="bacon"></div>',
         treeSanitizer: new NullTreeSanitizer());
     expect(anotherDiv.dataset.containsKey('eggs'), isTrue);
   });
 }