Temporary whitelist several cases of disk I/O on the UI threads in cros.

chrome/browser/chromeos/login/help_app_launcher.cc

 // Copyright (c) 2010 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 <string>
 
 #include "base/file_util.h"
 #include "base/logging.h"
+#include "base/threading/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/chromeos/login/help_app_launcher.h"
 #include "chrome/common/url_constants.h"
 #include "grit/generated_resources.h"
 #include "ui/base/l10n/l10n_util.h"
 
 namespace chromeos {
 
 namespace {
 const char kHelpTopicBasePath[] = "/usr/share/chromeos-assets/help/";
@@ skipping 13 matching lines @@
 // HelpApp, public:
 
 HelpAppLauncher::HelpAppLauncher(gfx::NativeWindow parent_window)
     : parent_window_(parent_window) {
 }
 
 // Checks whether local file exists at specified base path and
 // returns GURL instance for it. Otherwise returns an empty GURL.
 static GURL GetLocalFileUrl(const std::string& base_path,
                             const std::string& filename) {
+  // Checking for help dir existence causes us to do blocking IO on UI thread.
+  // Temporarily allow it until we fix http://crosbug.com/11105
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
   FilePath file_path(base_path + filename);
   if (file_util::PathExists(file_path)) {
     const std::string path_url = std::string(chrome::kFileScheme) +
          chrome::kStandardSchemeSeparator + file_path.value();
     return GURL(path_url);
   } else {
     return GURL();
   }
 }
 
@@ skipping 26 matching lines @@
             l10n_util::GetStringUTF16(IDS_LOGIN_OOBE_HELP_DIALOG_TITLE)),
         topic_url,
         LoginHtmlDialog::STYLE_BUBBLE));
   } else {
     dialog_->set_url(topic_url);
   }
   dialog_->Show();
 }
 
 }  // namespace chromeos