Implement SandboxFileWriter and rewrite FileWriterDelegate to use it

webkit/fileapi/webkit_fileapi.gypi

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'fileapi',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 56 matching lines @@
         'isolated_mount_point_provider.cc',
         'isolated_mount_point_provider.h',
         'local_file_util.cc',
         'local_file_util.h',
         'local_file_writer.cc',
         'local_file_writer.h',
         'native_file_util.cc',
         'native_file_util.h',
         'obfuscated_file_util.cc',
         'obfuscated_file_util.h',
+        'sandbox_file_writer.cc',
+        'sandbox_file_writer.h',
         'sandbox_mount_point_provider.cc',
         'sandbox_mount_point_provider.h',
         'test_mount_point_provider.cc',
         'test_mount_point_provider.h',
         'webfilewriter_base.cc',
         'webfilewriter_base.h',
       ],
       'conditions': [
         ['inside_chromium_build==0', {
           'dependencies': [
@@ skipping 10 matching lines @@
             '../chromeos/fileapi/file_util_async.h',
             '../chromeos/fileapi/remote_file_system_operation.cc',
             '../chromeos/fileapi/remote_file_system_operation.h',
             '../chromeos/fileapi/remote_file_system_proxy.h',
           ],
         }],
       ],
     },
   ],
 }