Add a switch to enable composited scrolling for frames and enable it on Android.

webkit/glue/webpreferences.cc

Index: webkit/glue/webpreferences.cc
diff --git a/webkit/glue/webpreferences.cc b/webkit/glue/webpreferences.cc
index d5dd85e5eadb6f05b3d5d0d7dc81ac774940d428..191b6edd5551c95fe9a6d1e1e0a475ea8ea2e023 100644
--- a/webkit/glue/webpreferences.cc
+++ b/webkit/glue/webpreferences.cc
@@ -85,6 +85,7 @@ WebPreferences::WebPreferences()
       show_fps_counter(false),
       accelerated_compositing_for_overflow_scroll_enabled(false),
       accelerated_compositing_for_scrollable_frames_enabled(false),
+      composited_scrolling_for_frames_enabled(false),
       show_paint_rects(false),
       render_vsync_enabled(true),
       asynchronous_spell_checking_enabled(true),
@@ -363,6 +364,10 @@ void WebPreferences::Apply(WebView* web_view) const {
   settings->setAcceleratedCompositingForScrollableFramesEnabled(
       accelerated_compositing_for_scrollable_frames_enabled);
 
+  // Enables composited scrolling for frames if requested on command line.
+  settings->setCompositedScrollingForFramesEnabled(
+      composited_scrolling_for_frames_enabled);
+
   // Display the current compositor tree as overlay if requested on
   // the command line
   settings->setShowPlatformLayerTree(show_composited_layer_tree);