chromeos: Makes mushrome use simplified display management

ash/aura/shell_port_classic.cc

Index: ash/aura/shell_port_classic.cc
diff --git a/ash/aura/shell_port_classic.cc b/ash/aura/shell_port_classic.cc
index e5e9760f8af7131430dda345d2c64f01ce62935e..eaba3c5a9cc7ea09641cd9a0bbd2e93b83985e2c 100644
--- a/ash/aura/shell_port_classic.cc
+++ b/ash/aura/shell_port_classic.cc
@@ -42,6 +42,8 @@
 
 #if defined(USE_X11)
 #include "ash/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.h"
+#include "ui/display/manager/chromeos/x11/native_display_delegate_x11.h"
+#include "ui/gfx/x/x11_types.h"  // nogncheck
 #endif
 
 #if defined(USE_OZONE)
@@ -264,7 +266,7 @@ ShellPortClassic::CreateNativeDisplayDelegate() {
 #if defined(USE_OZONE)
   return ui::OzonePlatform::GetInstance()->CreateNativeDisplayDelegate();
 #else
-  return nullptr;
+  return base::MakeUnique<display::NativeDisplayDelegateX11>();
 #endif
 }