Fix filesystem.retainEntry API to handle non-native directory.

chrome/test/data/extensions/api_test/file_browser/retain_entry/background.js

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * Retains a test directory.
+ * @return {Promise} Promise fulflled/rejected depending on the test result.
+ */
+function retainDirectory() {
+  return new Promise(function(fulfill) {
+    chrome.app.window.create('window.html', fulfill);
+  }).then(function(appWindow) {
+    return new Promise(function(fulfill, rejected) {
+      appWindow.contentWindow.chrome.fileSystem.chooseEntry(
+          {type: "openDirectory"},
+          fulfill);
+    });
+  }).then(function(selected) {
+    chrome.test.assertTrue(selected.isDirectory);
+    var id = chrome.fileSystem.retainEntry(selected);
+    chrome.test.assertTrue(!!id);
+    return new Promise(function(fulfill, rejected) {
+      chrome.fileSystem.isRestorable(id, fulfill);
+    }).then(function(restorable) {
+      chrome.test.assertTrue(restorable);
+      return new Promise(function(fulfill, rejected) {
+        chrome.storage.local.set({id: id}, fulfill);
+      });
+    });
+  }).then(function() {
+    chrome.runtime.reload();
+  });
+}
+
+/**
+ * Restores a test directory.
+ * @param {string} id ID of the test directory.
+ * @return {Promise} Promise fulflled/rejected depending on the test result.
+ */
+function restoreDirectory(id) {
+  return new Promise(function(fulfill) {
+    chrome.fileSystem.isRestorable(id, fulfill);
+  }).then(function(restorable) {
+    chrome.test.assertTrue(restorable);
+    return new Promise(function(fulfill) {
+      chrome.fileSystem.restoreEntry(id, fulfill);
+    });
+  }).then(function(directory) {
+    chrome.test.assertTrue(!!directory);
+    chrome.test.assertTrue(!!directory.isDirectory);
+  });
+}
+
+/**
+ * Tests to retain and to restore directory on the drive.
+ */
+function testRetainEntry() {
+  new Promise(function(fulfill) {
+    chrome.storage.local.get('id', fulfill);
+  }).then(function(values) {
+    if (!values.id)
+      return retainDirectory();
+    else
+      return restoreDirectory(values.id).then(chrome.test.callbackPass());
+  }).catch(function(error) {
+    chrome.test.fail(error.stack || error);
+  });
+}
+
+chrome.test.runTests([testRetainEntry]);