cros: Default to natural scrolling if the internal diplay is a touchscreen.

ash/display/display_change_observer_chromeos.cc

Index: ash/display/display_change_observer_chromeos.cc
diff --git a/ash/display/display_change_observer_chromeos.cc b/ash/display/display_change_observer_chromeos.cc
index 71bdfcd2d106d61c99eaadb344673a50909ef16f..0d67e45a7e19e6ae551176c417c52f3092c9a52e 100644
--- a/ash/display/display_change_observer_chromeos.cc
+++ b/ash/display/display_change_observer_chromeos.cc
@@ -197,6 +197,9 @@ void DisplayChangeObserver::OnDisplayModeChanged(
     displays.back().SetBounds(display_bounds);
     displays.back().set_native(true);
     displays.back().set_resolutions(resolutions);
+    displays.back().set_touch_support(
+        output.touch_device_id == 0 ? gfx::Display::TOUCH_SUPPORT_UNAVAILABLE :
+                                      gfx::Display::TOUCH_SUPPORT_AVAILABLE);
   }
 
   // DisplayManager can be null during the boot.