Re-enable DNS prefetch. This feature got disable accidentially in WebKit

webkit/glue/webpreferences.h

 // Copyright (c) 2011 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.
 //
 // A struct for managing webkit's settings.
 //
 // Adding new values to this class probably involves updating
 // WebKit::WebSettings, common/render_messages.cc, browser/tab_contents/
 // render_view_host_delegate_helper.cc, and browser/profiles/profile.cc.
 
@@ skipping 35 matching lines @@
   bool site_specific_quirks_enabled;
   bool shrinks_standalone_images_to_fit;
   bool uses_universal_detector;
   bool text_areas_are_resizable;
   bool java_enabled;
   bool allow_scripts_to_close_windows;
   bool uses_page_cache;
   bool remote_fonts_enabled;
   bool javascript_can_access_clipboard;
   bool xss_auditor_enabled;
+  // We don't use dns_prefetching_enabled to disable DNS prefetching.  Instead,
+  // we disable the feature at a lower layer so that we catch non-WebKit uses
+  // of DNS prefetch as well.
+  bool dns_prefetching_enabled;
   bool local_storage_enabled;
   bool databases_enabled;
   bool application_cache_enabled;
   bool tabs_to_links;
   bool caret_browsing_enabled;
   bool hyperlink_auditing_enabled;
 
   bool user_style_sheet_enabled;
   GURL user_style_sheet_location;
   bool author_and_user_styles_enabled;
@@ skipping 24 matching lines @@
   // We try to keep the default values the same as the default values in
   // chrome, except for the cases where it would require lots of extra work for
   // the embedder to use the same default value.
   WebPreferences();
   ~WebPreferences();
 
   void Apply(WebKit::WebView* web_view) const;
 };
 
 #endif  // WEBKIT_GLUE_WEBPREFERENCES_H__