respect --force-compositing-mode for chrome: pages

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 f605fa15f8798bcc4c746340d07fc8c0d75343d7..e4f1386d76577fbd6d01152063691710414d2723 100644
--- a/chrome/browser/tab_contents/render_view_host_delegate_helper.cc
+++ b/chrome/browser/tab_contents/render_view_host_delegate_helper.cc
@@ -403,6 +403,8 @@ WebPreferences RenderViewHostDelegateHelper::GetWebkitPrefs(
         !command_line.HasSwitch(switches::kDisableAcceleratedCompositing);
     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);