Add a switch to enable compositing for scrollable frames.

webkit/glue/webpreferences.cc

Index: webkit/glue/webpreferences.cc
diff --git a/webkit/glue/webpreferences.cc b/webkit/glue/webpreferences.cc
index 82e75e65b691beef3b3dc37e08e53007b038d20d..d6c5be918e0cd7bcbfdb9b7ca96c167115a9a697 100644
--- a/webkit/glue/webpreferences.cc
+++ b/webkit/glue/webpreferences.cc
@@ -82,6 +82,7 @@ WebPreferences::WebPreferences()
       show_composited_layer_tree(false),
       show_fps_counter(false),
       accelerated_compositing_for_overflow_scroll_enabled(false),
+      accelerated_compositing_for_scrollable_frames_enabled(false),
       show_paint_rects(false),
       render_vsync_enabled(true),
       asynchronous_spell_checking_enabled(true),
@@ -344,6 +345,11 @@ void WebPreferences::Apply(WebView* web_view) const {
   settings->setAcceleratedCompositingForOverflowScrollEnabled(
       accelerated_compositing_for_overflow_scroll_enabled);
 
+  // Enables accelerated compositing for scrollable frames if requested on
+  // command line.
+  settings->setAcceleratedCompositingForScrollableFramesEnabled(
+      accelerated_compositing_for_scrollable_frames_enabled);
+
   // Display the current compositor tree as overlay if requested on
   // the command line
   settings->setShowPlatformLayerTree(show_composited_layer_tree);