Add isWritableFileEntry to the fileSystem API

chrome/common/extensions/api/file_system.idl

 // 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.
 
 // File-level comment to appease parser. Eventually this will not be necessary.
 
 namespace fileSystem {
   dictionary ChooseFileOptions {
     // Type of the prompt to show. Valid types are 'openFile',
     // 'openWritableFile' or 'saveFile'.
     //
     // Both 'openFile' and 'openWritableFile' will prompt the user to open an
     // existing file, with 'openFile' returning a read-only FileEntry on
     // success. 'saveFile' will prompt the user to choose an existing file or
     // a new file, and will return a writable FileEntry.
     // Calls to chooseFile with either 'openWritableFile' or 'saveFile' will
     // fail unless the application has the fileSystemWrite permission.
     //
     // The default is 'openFile'.
     DOMString? type;
 
     // The suggested file name that will be presented to the user as the
     // default name to read or write. This is optional.
     DOMString? suggestedName;
   };
   callback GetDisplayPathCallback = void (DOMString displayPath);
-  callback FileEntryCallback = void ([instanceOf=fileEntry] object fileEntry);
+  callback FileEntryCallback = void ([instanceOf=FileEntry] object fileEntry);
+  callback IsWritableCallback = void (boolean isWritable);
 
   interface Functions {
     // Get the display path of a FileEntry object. The display path is based on
     // the full path of the file on the local file system, but may be made more
     // readable for display purposes.
     static void getDisplayPath([instanceOf=FileEntry] object fileEntry,
                                GetDisplayPathCallback callback);
 
     // Get a writable FileEntry from another FileEntry. This call will fail
     // if the application does not have the fileSystemWrite permission.
     static void getWritableFileEntry([instanceOf=FileEntry] object fileEntry,
                                      FileEntryCallback callback);
 
+    // Gets whether this FileEntry is writable or not.
+    static void isWritableFileEntry([instanceOf=FileEntry] object fileEntry,
+                                    IsWritableCallback callback);
+
     // Ask the user to choose a file.
     static void chooseFile(optional ChooseFileOptions options,
                            FileEntryCallback callback);
   };
 };