mus: Changes SetDisplayRoot() to create actual display

services/ui/display/screen_manager_ozone_external.cc

Index: services/ui/display/screen_manager_ozone_external.cc
diff --git a/services/ui/display/screen_manager_ozone_external.cc b/services/ui/display/screen_manager_ozone_external.cc
index 45a50277243121d9913a5b5ea897b478f7458a0a..5bc97b3df96648cdcc8d5654ca932639b9dcb636 100644
--- a/services/ui/display/screen_manager_ozone_external.cc
+++ b/services/ui/display/screen_manager_ozone_external.cc
@@ -7,6 +7,7 @@
 #include <memory>
 
 #include "services/service_manager/public/cpp/binder_registry.h"
+#include "ui/display/screen_base.h"
 #include "ui/display/types/display_constants.h"
 
 namespace display {
@@ -16,7 +17,8 @@ std::unique_ptr<ScreenManager> ScreenManager::Create() {
   return base::MakeUnique<ScreenManagerOzoneExternal>();
 }
 
-ScreenManagerOzoneExternal::ScreenManagerOzoneExternal() {}
+ScreenManagerOzoneExternal::ScreenManagerOzoneExternal()
+    : screen_(base::MakeUnique<display::ScreenBase>()) {}
 
 ScreenManagerOzoneExternal::~ScreenManagerOzoneExternal() {}
 
@@ -27,4 +29,8 @@ void ScreenManagerOzoneExternal::Init(ScreenManagerDelegate* delegate) {}
 
 void ScreenManagerOzoneExternal::RequestCloseDisplay(int64_t display_id) {}
 
+display::ScreenBase* ScreenManagerOzoneExternal::GetScreen() {
+  return screen_.get();
+}
+
 }  // namespace display