[NaCl SDK] nacl_io: Add doc for html5fs param "filesystem_resource"

native_client_sdk/src/libraries/nacl_io/nacl_io.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 LIBRARIES_NACL_IO_NACL_IO_H_
 #define LIBRARIES_NACL_IO_NACL_IO_H_
 
 #include <ppapi/c/pp_instance.h>
 #include <ppapi/c/ppb.h>
 
@@ skipping 66 matching lines @@
  *   "html5fs": A filesystem that uses PPAPI FileSystem interface, which can be
  *              read in JavaScript via the HTML5 FileSystem API. This filesystem
  *              provides the use of persistent storage. Please read the
  *              documentation in ppapi/c/ppb_file_system.h for more information.
  *     source: Unused.
  *     data: A string of parameters:
  *       "type": Which type of filesystem to mount. Valid values are
  *           "PERSISTENT" and "TEMPORARY". The default is "PERSISTENT".
  *       "expected_size": The expected file-system size. Note that this does
  *           not request quota -- you must do that from JavaScript.
+ *       "filesystem_resource": If specified, this is a string that contains
+ *           the integer ID of the Filesystem resource to use instead of
+ *           creating a new one. The "type" and "expected_size" parameters are
+ *           ignored in this case. This parameter is useful when you pass a
+ *           Filesystem resource from JavaScript, but still want to be able to
+ *           call open/read/write/etc.
  *
  *   "httpfs": A filesystem that reads from a URL via HTTP.
  *     source: The root URL to read from. All paths read from this filesystem
  *             will be appended to this root.
  *             e.g. If source == "http://example.com/path", reading from
  *             "foo/bar.txt" will attempt to read from the URL
  *             "http://example.com/path/foo/bar.txt".
  *     data: A string of parameters:
  *       "allow_cross_origin_requests": If "true", then reads from this
  *           filesystem will follow the CORS standard for cross-origin requests.
@@ skipping 80 matching lines @@
  *
  * @param[in] fs_type The name of the filesystem type; the same identifier that
  *     was passed to nacl_io_register_fs_type().
  * @return 0 on success, -1 on failure (with errno set).
  */
 int nacl_io_unregister_fs_type(const char* fs_type);
 
 EXTERN_C_END
 
 #endif /* LIBRARIES_NACL_IO_NACL_IO_H_ */