Add an --enable-container-culling commandline flag.

content/renderer/web_preferences.cc

Index: content/renderer/web_preferences.cc
diff --git a/content/renderer/web_preferences.cc b/content/renderer/web_preferences.cc
index 6ac5d538eecafd9e9fb02de5a09e3e77efc80bd7..78974a60f0399c520f14a6c4914b303b160ac94b 100644
--- a/content/renderer/web_preferences.cc
+++ b/content/renderer/web_preferences.cc
@@ -231,6 +231,9 @@ void ApplyWebPreferences(const WebPreferences& prefs, WebView* web_view) {
   // Enable deferred filter rendering if requested on the command line.
   settings->setDeferredFiltersEnabled(prefs.deferred_filters_enabled);
 
+  // Enable container culling if requested on the command line.
+  settings->setContainerCullingEnabled(prefs.container_culling_enabled);
+
   // Enable gesture tap highlight if requested on the command line.
   settings->setGestureTapHighlightEnabled(prefs.gesture_tap_highlight_enabled);