Implement cursor compositing mode on Ash

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 4d15cd3083da3d815489318c62031e64606d1e2c..fd249dcf15e1c4d72135bfdc184e30e43d64dada 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -537,6 +537,10 @@ class ASH_EXPORT Shell
   // returned object.
   ash::FirstRunHelper* CreateFirstRunHelper();
 
+  // Toggles cursor compositing on/off. Native cursor is disabled when cursor
+  // compositing is enabled, and vice versa.
+  void SetCursorCompositingEnabled(bool enabled);
+
   StickyKeysController* sticky_keys_controller() {
     return sticky_keys_controller_.get();
   }