Add support for persistent file access in apps.

chrome/renderer/resources/extensions/entry_id_manager.js

 // Copyright (c) 2013 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.
 
+var fileSystemNatives = requireNative('file_system_natives');
+
 var nameToIds = {};
 var idsToEntries = {};
 
 function computeName(entry) {
   return entry.filesystem.name + ':' + entry.fullPath;
 }
 
+function computeId(entry) {
+  var fileSystemId = fileSystemNatives.CrackIsolatedFileSystemName(
+      entry.filesystem.name);
+  if (!fileSystemId)
+    return null;
+  // Strip the leading '/' from the path.
+  return fileSystemId + ':' + entry.fullPath.slice(1);
+}
+
 function registerEntry(id, entry) {
   var name = computeName(entry);
   nameToIds[name] = id;
   idsToEntries[id] = entry;
-};
+}
 
 function getEntryId(entry) {
   var name = null;
   try {
     name = computeName(entry);
   } catch(e) {
     return null;
   }
-  return nameToIds[name];
+  var id = nameToIds[name];
+  if (id != null)
+    return id;
+
+  // If an entry has not been registered, compute its id and register it.
+  id = computeId(entry);
+  registerEntry(id, entry);
+  return id;
 }
 
 function getEntryById(id) {
   return idsToEntries[id];
 }
 
 exports.registerEntry = registerEntry;
 exports.getEntryId = getEntryId;
 exports.getEntryById = getEntryById;