Turn on file access checks on Win.

chrome/browser/download/download_util.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.
 //
 // Download utility implementation
 
 #include "chrome/browser/download/download_util.h"
 
 #if defined(OS_WIN)
 #include <shobjidl.h>
 #endif
 #include <string>
 
 #include "app/l10n_util.h"
 #include "app/resource_bundle.h"
 #include "base/file_util.h"
 #include "base/i18n/rtl.h"
 #include "base/i18n/time_formatting.h"
 #include "base/path_service.h"
 #include "base/singleton.h"
 #include "base/string16.h"
 #include "base/string_number_conversions.h"
 #include "base/sys_string_conversions.h"
+#include "base/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "base/win/windows_version.h"
 #include "chrome/browser/browser.h"
 #include "chrome/browser/browser_list.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/browser_thread.h"
 #include "chrome/browser/download/download_item.h"
 #include "chrome/browser/download/download_item_model.h"
 #include "chrome/browser/download/download_manager.h"
@@ skipping 109 matching lines @@
 
 #if defined(OS_WIN)
   static const FilePath::CharType default_extension[] =
       FILE_PATH_LITERAL("download");
 
   // Rename shell-integrated extensions.
   if (win_util::IsShellIntegratedExtension(extension))
     extension.assign(default_extension);
 #endif
 
-  if (extension.empty())
+  if (extension.empty()) {
+    // The GetPreferredExtensionForMimeType call will end up going to disk.  Do
+    // this on another thread to avoid slowing the IO thread.
+    // http://crbug.com/61827
+    base::ThreadRestrictions::ScopedAllowIO allow_io;
     net::GetPreferredExtensionForMimeType(mime_type, &extension);
+  }
 
   generated_extension->swap(extension);
 }
 
 void GenerateFileNameFromInfo(DownloadCreateInfo* info,
                               FilePath* generated_name) {
   GenerateFileName(GURL(info->url),
                    info->content_disposition,
                    info->referrer_charset,
                    info->mime_type,
@@ skipping 560 matching lines @@
     ExtensionsService* service = profile->GetExtensionsService();
     if (!service ||
         !service->IsDownloadFromGallery(info->url, info->referrer_url)) {
       return true;
     }
   }
   return false;
 }
 
 }  // namespace download_util