Add command line switch for enabling threaded compositing

chrome/browser/tab_contents/render_view_host_delegate_helper.cc

 // 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.
 
 #include "chrome/browser/tab_contents/render_view_host_delegate_helper.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/string_util.h"
@@ skipping 423 matching lines @@
         command_line.HasSwitch(switches::kAllowFileAccessFromFiles);
     web_prefs.show_composited_layer_borders =
         command_line.HasSwitch(switches::kShowCompositedLayerBorders);
     web_prefs.show_composited_layer_tree =
         command_line.HasSwitch(switches::kShowCompositedLayerTree);
     web_prefs.show_fps_counter =
         command_line.HasSwitch(switches::kShowFPSCounter);
     web_prefs.accelerated_compositing_enabled =
         GpuProcessHost::gpu_enabled() &&
         !command_line.HasSwitch(switches::kDisableAcceleratedCompositing);
+    web_prefs.threaded_compositing_enabled =
+        command_line.HasSwitch(switches::kEnableThreadedCompositing);
     web_prefs.force_compositing_mode =
         command_line.HasSwitch(switches::kForceCompositingMode);
     web_prefs.allow_webui_compositing =
         command_line.HasSwitch(switches::kAllowWebUICompositing);
     web_prefs.accelerated_2d_canvas_enabled =
         GpuProcessHost::gpu_enabled() &&
         !command_line.HasSwitch(switches::kDisableAccelerated2dCanvas);
     web_prefs.accelerated_drawing_enabled =
         GpuProcessHost::gpu_enabled() &&
         command_line.HasSwitch(switches::kEnableAcceleratedDrawing);
@@ skipping 89 matching lines @@
   DictionaryValue* inspector_settings = update.Get();
   inspector_settings->SetWithoutPathExpansion(key,
                                               Value::CreateStringValue(value));
 }
 
 void RenderViewHostDelegateHelper::ClearInspectorSettings(
     content::BrowserContext* browser_context) {
   Profile::FromBrowserContext(browser_context)->GetPrefs()->
       ClearPref(prefs::kWebKitInspectorSettings);
 }