Add support for directory access to the file system API.

chrome/test/data/extensions/api_test/file_system/retain_directory/test.js

Index: chrome/test/data/extensions/api_test/file_system/retain_directory/test.js
diff --git a/chrome/test/data/extensions/api_test/file_system/retain_entry/test.js b/chrome/test/data/extensions/api_test/file_system/retain_directory/test.js
similarity index 68%
copy from chrome/test/data/extensions/api_test/file_system/retain_entry/test.js
copy to chrome/test/data/extensions/api_test/file_system/retain_directory/test.js
index 9555e8e52d33d28fb2a812c6d79c02c2fa24d139..03f03ac75eb79b9c4cc8528e7eeb710d37b0d43a 100644
--- a/chrome/test/data/extensions/api_test/file_system/retain_entry/test.js
+++ b/chrome/test/data/extensions/api_test/file_system/retain_directory/test.js
@@ -19,8 +19,16 @@ chrome.test.runTests([
           chrome.test.assertEq(restoredEntry, entry);
           chrome.test.assertEq(
               chrome.fileSystem.retainEntry(restoredEntry), id);
-          checkEntry(restoredEntry, 'writable.txt', false /* isNew */,
-            false /*shouldBeWritable */);
+          var reader = entry.createReader();
+          reader.readEntries(chrome.test.callback(function(entries) {
+            chrome.test.assertEq(entries.length, 1);
+            checkEntry(entries[0], 'open_existing.txt', false, false);
+          }));
+          entry.getFile(
+              'open_existing.txt', {},
+              chrome.test.callbackPass(function(entry) {
+            checkEntry(entry, 'open_existing.txt', false, false);
+          }));
         }));
       });
     }));