[content shell] add scoped allow io to allow for reading files during layout tests

content/shell/shell_message_filter.cc

 // Copyright (c) 2013 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/shell/shell_message_filter.h"
 
 #include "base/file_util.h"
+#include "base/threading/thread_restrictions.h"
 #include "content/public/browser/child_process_security_policy.h"
 #include "content/shell/shell_messages.h"
 #include "content/shell/shell_network_delegate.h"
 #include "net/base/net_errors.h"
 #include "webkit/database/database_tracker.h"
 #include "webkit/fileapi/isolated_context.h"
 #include "webkit/quota/quota_manager.h"
 
 namespace content {
 
@@ skipping 26 matching lines @@
     IPC_MESSAGE_HANDLER(ShellViewHostMsg_SetDatabaseQuota, OnSetDatabaseQuota)
     IPC_MESSAGE_HANDLER(ShellViewHostMsg_AcceptAllCookies, OnAcceptAllCookies)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
   return handled;
 }
 
 void ShellMessageFilter::OnReadFileToString(const base::FilePath& local_file,
                                             std::string* contents) {
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
   file_util::ReadFileToString(local_file, contents);
 }
 
 void ShellMessageFilter::OnRegisterIsolatedFileSystem(
     const std::vector<base::FilePath>& absolute_filenames,
     std::string* filesystem_id) {
   fileapi::IsolatedContext::FileInfoSet files;
   ChildProcessSecurityPolicy* policy =
       ChildProcessSecurityPolicy::GetInstance();
   for (size_t i = 0; i < absolute_filenames.size(); ++i) {
@@ skipping 16 matching lines @@
   quota_manager_->SetTemporaryGlobalOverrideQuota(
       quota * quota::QuotaManager::kPerHostTemporaryPortion,
       quota::QuotaCallback());
 }
 
 void ShellMessageFilter::OnAcceptAllCookies(bool accept) {
   ShellNetworkDelegate::SetAcceptAllCookies(accept);
 }
 
 }  // namespace content