Revert "Removed asyncTest and improved comments."

tests/html/fileapi_test.dart

 #library('fileapi');
 #import('../../lib/unittest/unittest.dart');
 #import('../../lib/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   useHtmlConfiguration();
   window.webkitRequestFileSystem(Window.TEMPORARY, 100, (fs) {
     // FIXME: add types to callback arguments after migration to wrapperless dart:html.
-    test('getDirectory', () {
+    asyncTest('getDirectory', 2, () {
       Expect.throws(() => fs.root.getDirectory('directory1', {'x': true}, (e) {}));
 
       fs.root.getDirectory(
           'directory2',
           flags: {},
-          successCallback:
-            (e) => guardAsync(() => Expect.fail('Should not be reached')),
-          errorCallback:
-            expectAsync1((e) => Expect.equals(FileError.NOT_FOUND_ERR, e.code))
-          );
+          successCallback: (e) {
+            Expect.fail('Should not be reached');
+            callbackDone();
+          },
+          errorCallback: (e) {
+            Expect.equals(FileError.NOT_FOUND_ERR, e.code);
+            callbackDone();
+          });
 
       fs.root.getDirectory(
           'directory3',
           flags: {'create': true},
-          successCallback:
-            expectAsync1((e) => Expect.equals('directory3', e.name)),
-          errorCallback:
-            (e) => guardAsync(() => Expect.fail('Got file error: ${e.code}'))
-          );
+          successCallback: (e) {
+            Expect.equals('directory3', e.name);
+            callbackDone();
+          },
+          errorCallback: (e) {
+            Expect.fail('Got file error: ${e.code}');
+            callbackDone();
+          });
     });
 
-    test('getFile', () {
+    asyncTest('getFile', 2, () {
       Expect.throws(() => fs.root.getFile('file1', {'x': true}, (e) {}));
 
       fs.root.getDirectory(
           'file2',
           flags: {},
-          successCallback:
-            (e) => guardAsync(() => Expect.fail('Should not be reached')),
-          errorCallback:
-            expectAsync1((e) => Expect.equals(FileError.NOT_FOUND_ERR, e.code))
-          );
+          successCallback: (e) {
+            Expect.fail('Should not be reached');
+            callbackDone();
+          },
+          errorCallback: (e) {
+            Expect.equals(FileError.NOT_FOUND_ERR, e.code);
+            callbackDone();
+          });
 
       fs.root.getDirectory(
           'file3',
           flags: {'create': true},
-          successCallback:
-            expectAsync1((e) => Expect.equals('file3', e.name)),
-          errorCallback:
-            (e) => guardAsync(() => Expect.fail('Got file error: ${e.code}'))
-          );
+          successCallback: (e) {
+            Expect.equals('file3', e.name);
+            callbackDone();
+          },
+          errorCallback: (e) {
+            Expect.fail('Got file error: ${e.code}');
+            callbackDone();
+          });
     });
   });
 }