Add command line switch for enabling threaded compositing

webkit/glue/webpreferences.cc

Index: webkit/glue/webpreferences.cc
diff --git a/webkit/glue/webpreferences.cc b/webkit/glue/webpreferences.cc
index 08fd7dbc7d9fd5ea82d112e2bc9639685a772421..a55413721e7e8481948c2f381c826a181c2431fa 100644
--- a/webkit/glue/webpreferences.cc
+++ b/webkit/glue/webpreferences.cc
@@ -74,6 +74,7 @@ WebPreferences::WebPreferences()
       show_fps_counter(false),
       asynchronous_spell_checking_enabled(true),
       accelerated_compositing_enabled(false),
+      threaded_compositing_enabled(false),
       force_compositing_mode(false),
       allow_webui_compositing(false),
       composite_to_texture_enabled(false),
@@ -249,6 +250,8 @@ void WebPreferences::Apply(WebView* web_view) const {
   // Enable gpu-accelerated compositing if requested on the command line.
   settings->setAcceleratedCompositingEnabled(accelerated_compositing_enabled);
 
+  settings->setUseThreadedCompositor(threaded_compositing_enabled);
+
   // Always enter compositing if requested on the command line.
   settings->setForceCompositingMode(force_compositing_mode);