Make Isolated file system writable only if it is configured so

content/browser/child_process_security_policy_impl.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.
 
 #include "content/browser/child_process_security_policy_impl.h"
 
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/platform_file.h"
@@ skipping 342 matching lines @@
   state->second->RevokeAllPermissionsForFile(file);
 }
 
 void ChildProcessSecurityPolicyImpl::GrantReadFileSystem(
     int child_id, const std::string& filesystem_id) {
   GrantPermissionsForFileSystem(child_id, filesystem_id, kReadFilePermissions);
 }
 
 void ChildProcessSecurityPolicyImpl::GrantReadWriteFileSystem(
     int child_id, const std::string& filesystem_id) {
+  fileapi::IsolatedContext::GetInstance()->SetWritable(filesystem_id, true);
   GrantPermissionsForFileSystem(child_id, filesystem_id,
                                 kReadFilePermissions |
                                 kWriteFilePermissions);
 }
 
 void ChildProcessSecurityPolicyImpl::GrantScheme(int child_id,
                                                  const std::string& scheme) {
   base::AutoLock lock(lock_);
 
   SecurityStateMap::iterator state = security_state_.find(child_id);
@@ skipping 192 matching lines @@
     int child_id,
     const std::string& filesystem_id,
     int permission) {
   base::AutoLock lock(lock_);
 
   SecurityStateMap::iterator state = security_state_.find(child_id);
   if (state == security_state_.end())
     return false;
   return state->second->HasPermissionsForFileSystem(filesystem_id, permission);
 }