Dartifying dart:html type names.

tests/html/fileapi_test.dart

 library fileapi;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 void fail(message) {
   guardAsync(() {
     expect(false, isTrue, reason: message);
   });
 }
 
-DOMFileSystem fs;
+FileSystem fs;
 
 main() {
   useHtmlConfiguration();
   test('getFileSystem', () {
     window.webkitRequestFileSystem(LocalWindow.TEMPORARY, 100, expectAsync1(
-      (DOMFileSystem fileSystem) {
+      (FileSystem fileSystem) {
         fs = fileSystem;
       }),
       (e) {
         fail('Got file error: ${e.code}');
       });
   });
   group('getDirectory', () {
 
     test('directoryDoesntExist', () {
       fs.root.getDirectory(
@@ skipping 41 matching lines @@
           successCallback: expectAsync1((FileEntry e) {
             expect(e.name, equals('file4'));
             expect(e.isFile, isTrue);
           }),
           errorCallback: (e) {
             fail('Got file error: ${e.code}');
           });
       });
   });
 }