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

test/codegen/lib/html/websocket_test.dart

+library WebSocketTest;
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_individual_config.dart';
+import 'dart:html';
+
+main() {
+
+  useHtmlIndividualConfiguration();
+
+  group('supported', () {
+    test('supported', () {
+      expect(WebSocket.supported, true);
+    });
+  });
+
+  group('websocket', () {
+    var isWebSocket = predicate((x) => x is WebSocket, 'is a WebSocket');
+    var expectation = WebSocket.supported ? returnsNormally : throws;
+
+    test('constructorTest', () {
+      expect(() {
+        var socket = new WebSocket('ws://localhost/ws', 'chat');
+        expect(socket, isNotNull);
+        expect(socket, isWebSocket);
+        }, expectation);
+    });
+
+    if (WebSocket.supported) {
+      test('echo', () {
+        var socket = new WebSocket('ws://${window.location.host}/ws');
+
+        socket.onOpen.first.then((_) {
+          socket.send('hello!');
+        });
+
+        return socket.onMessage.first.then((MessageEvent e) {
+          expect(e.data, 'hello!');
+          socket.close();
+        });
+      });
+
+      test('error handling', () {
+        var socket = new WebSocket('ws://${window.location.host}/ws');
+        socket.onOpen.first.then((_) => socket.send('close-with-error'));
+        return socket.onError.first.then((e) {
+          print('$e was caught, yay!');
+          socket.close();
+        });
+      });
+    }
+  });
+}