Add support for persistent file access in apps.

chrome/browser/extensions/api/file_system/file_system_api.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_FILE_SYSTEM_FILE_SYSTEM_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_FILE_SYSTEM_FILE_SYSTEM_API_H_
 
 #include "chrome/browser/extensions/extension_function.h"
 #include "chrome/common/extensions/api/file_system.h"
 #include "ui/shell_dialogs/select_file_dialog.h"
@@ skipping 26 matching lines @@
   // the file is not a link. If it succeeds it proceeds to
   // RegisterFileSystemAndSendResponse, otherwise to HandleWritableFileError.
   void CheckWritableFile(const base::FilePath& path);
 
   // This will finish the choose file process. This is either called directly
   // from FileSelected, or from CreateFileIfNecessary. It is called on the UI
   // thread.
   void RegisterFileSystemAndSendResponse(const base::FilePath& path,
                                          EntryType entry_type);
 
+  // This will finish the choose file process. This is either called directly
+  // from FileSelected, or from CreateFileIfNecessary. It is called on the UI
+  // thread. |id_override| specifies the id to send in the response instead of
+  // the generated id.

[koz (OOO until 15th September), 2013/05/23 07:32:22]

Could you expand a bit on why it would be useful to override the generated id?

[Sam McNally, 2013/05/24 00:46:03]

Done.

+  void RegisterFileSystemAndSendResponseWithIdOverride(
+      const base::FilePath& path,
+      EntryType entry_type,
+      const std::string& id_override);
+
   // called on the UI thread if there is a problem checking a writable file.
   void HandleWritableFileError();
 };
 
 class FileSystemGetWritableEntryFunction : public FileSystemEntryFunction {
  public:
   DECLARE_EXTENSION_FUNCTION("fileSystem.getWritableEntry",
                              FILESYSTEM_GETWRITABLEENTRY)
 
  protected:
@@ skipping 51 matching lines @@
   void SetInitialPathOnFileThread(const base::FilePath& suggested_name,
                                   const base::FilePath& previous_path);
 
   // FileSelected and FileSelectionCanceled are called by the file picker.
   void FileSelected(const base::FilePath& path, EntryType entry_type);
   void FileSelectionCanceled();
 
   base::FilePath initial_path_;
 };
 
+class FileSystemRetainEntryFunction : public SyncExtensionFunction {
+ public:
+  DECLARE_EXTENSION_FUNCTION("fileSystem.retainEntry", FILESYSTEM_RETAINENTRY)
+
+ protected:
+  virtual ~FileSystemRetainEntryFunction() {}
+  virtual bool RunImpl() OVERRIDE;
+
+ private:
+  // Retains the file entry referenced by |entry_id| in apps::SavedFilesService.
+  // |entry_id| must refer to an entry in an isolated file system.
+  bool RetainFileEntry(const std::string& entry_id);
+};
+
+class FileSystemIsRestorableFunction : public SyncExtensionFunction {
+ public:
+  DECLARE_EXTENSION_FUNCTION("fileSystem.isRestorable", FILESYSTEM_ISRESTORABLE)
+
+ protected:
+  virtual ~FileSystemIsRestorableFunction() {}
+  virtual bool RunImpl() OVERRIDE;
+};
+
+class FileSystemRestoreEntryFunction : public FileSystemEntryFunction {
+ public:
+  DECLARE_EXTENSION_FUNCTION("fileSystem.restoreEntry", FILESYSTEM_RESTOREENTRY)
+
+ protected:
+  virtual ~FileSystemRestoreEntryFunction() {}
+  virtual bool RunImpl() OVERRIDE;
+};
+
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_FILE_SYSTEM_FILE_SYSTEM_API_H_