PPAPI: Add Quota info to PPB_FileSystem::Open doc

ppapi/api/ppb_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.
  */
 
 /**
  * This file defines the API to create a file system associated with a file.
  */
 
 label Chrome {
@@ skipping 28 matching lines @@
    * invalid or some type other than <code>PPB_FileSystem</code>.
    */
   PP_Bool IsFileSystem([in] PP_Resource resource);
 
   /**
    * Open() opens the file system. A file system must be opened before running
    * any other operation on it.
    *
    * @param[in] file_system A <code>PP_Resource</code> corresponding to a file
    * system.
-   * @param[in] expected_size The expected size of the file system.
+   *
+   * @param[in] expected_size The expected size of the file system. Note that
+   * this does not request quota; to do that, you must either invoke
+   * requestQuota from JavaScript:
+   * http://www.html5rocks.com/en/tutorials/file/filesystem/#toc-requesting-quota
+   * or set the unlimitedStorage permission for Chrome Web Store apps:
+   * http://code.google.com/chrome/extensions/manifest.html#permissions
+   *
    * @param[in] callback A <code>PP_CompletionCallback</code> to be called upon
    * completion of Open().
    *
    * @return An int32_t containing an error code from <code>pp_errors.h</code>.
    */
   int32_t Open([in] PP_Resource file_system,
                [in] int64_t expected_size,
                [in] PP_CompletionCallback callback);
 
   /**
    * GetType() returns the type of the provided file system.
    *
    * @param[in] file_system A <code>PP_Resource</code> corresponding to a file
    * system.
    *
    * @return A <code>PP_FileSystemType</code> with the file system type if
    * valid or <code>PP_FILESYSTEMTYPE_INVALID</code> if the provided resource
    * is not a valid file system. It is valid to call this function even before
    * Open() completes.
    */
   PP_FileSystemType GetType([in] PP_Resource file_system);
 };