Added a switch to enable a unified text checker and asynchronous

chrome/browser/tab_contents/render_view_host_delegate_helper.cc

Index: chrome/browser/tab_contents/render_view_host_delegate_helper.cc
diff --git a/chrome/browser/tab_contents/render_view_host_delegate_helper.cc b/chrome/browser/tab_contents/render_view_host_delegate_helper.cc
index 704c22aefb2d4ab6cc15155495cbb8658d42b6df..a17a60bdfda45c40ee08519774bc995094e256c6 100644
--- a/chrome/browser/tab_contents/render_view_host_delegate_helper.cc
+++ b/chrome/browser/tab_contents/render_view_host_delegate_helper.cc
@@ -505,6 +505,9 @@ WebPreferences RenderViewHostDelegateHelper::GetWebkitPrefs(
 
     web_prefs.visual_word_movement_enabled =
         command_line.HasSwitch(switches::kEnableVisualWordMovement);
+
+    web_prefs.unified_textchecker_enabled =
+        command_line.HasSwitch(switches::kExperimentalSpellcheckerFeatures);
   }
 
   {  // Certain GPU features might have been blacklisted.