Update the child process security policy to use explicit permission grants.

chrome/browser/chromeos/extensions/file_manager/file_browser_handler_api.cc

 // 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.
 
 // The file contains the implementation of
 // fileBrowserHandlerInternal.selectFile extension function.
 // When invoked, the function does the following:
 //  - Verifies that the extension function was invoked as a result of user
 //    gesture.
 //  - Display 'save as' dialog using FileSelectorImpl which waits for the user
@@ skipping 363 matching lines @@
 
   external_provider->GetVirtualPath(full_path_, &virtual_path_);
   DCHECK(!virtual_path_.empty());
 
   // Grant access to this particular file to target extension. This will
   // ensure that the target extension can access only this FS entry and
   // prevent from traversing FS hierarchy upward.
   external_provider->GrantFileAccessToExtension(extension_id(), virtual_path_);
 
   // Grant access to the selected file to target extensions render view process.
-  content::ChildProcessSecurityPolicy::GetInstance()->GrantPermissionsForFile(
-      render_view_host()->GetProcess()->GetID(),
-      full_path_,
-      file_handler_util::GetReadWritePermissions());
+  content::ChildProcessSecurityPolicy::GetInstance()->GrantCreateReadWriteFile(
+      render_view_host()->GetProcess()->GetID(), full_path_);
 }
 
 void FileBrowserHandlerInternalSelectFileFunction::Respond(bool success) {
   scoped_ptr<SelectFile::Results::Result> result(
       new SelectFile::Results::Result());
   result->success = success;
 
   // If the file was selected, add 'entry' object which will be later used to
   // create a FileEntry instance for the selected file.
   if (success) {
     result->entry.reset(new FileEntryInfo());
     result->entry->file_system_name = file_system_name_;
     result->entry->file_system_root = file_system_root_.spec();
     result->entry->file_full_path = "/" + virtual_path_.AsUTF8Unsafe();
     result->entry->file_is_directory = false;
   }
 
   results_ = SelectFile::Results::Create(*result);
   SendResponse(true);
 }