mus: Changes SetDisplayRoot() to create actual display

services/ui/display/screen_manager_stub_internal.cc

Index: services/ui/display/screen_manager_stub_internal.cc
diff --git a/services/ui/display/screen_manager_stub_internal.cc b/services/ui/display/screen_manager_stub_internal.cc
index e513b004c80eb5aff896d6af6f7fdd17a5d9611e..335d343f28309e2fe5655e519bd0ee8189c7d934 100644
--- a/services/ui/display/screen_manager_stub_internal.cc
+++ b/services/ui/display/screen_manager_stub_internal.cc
@@ -12,6 +12,7 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "services/service_manager/public/cpp/binder_registry.h"
 #include "services/ui/display/viewport_metrics.h"
+#include "ui/display/screen_base.h"
 #include "ui/gfx/geometry/dip_util.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
@@ -46,7 +47,8 @@ std::unique_ptr<ScreenManager> ScreenManager::Create() {
 }
 
 ScreenManagerStubInternal::ScreenManagerStubInternal()
-    : weak_ptr_factory_(this) {}
+    : screen_(base::MakeUnique<display::ScreenBase>()),
+      weak_ptr_factory_(this) {}
 
 ScreenManagerStubInternal::~ScreenManagerStubInternal() {}
 
@@ -80,4 +82,8 @@ void ScreenManagerStubInternal::RequestCloseDisplay(int64_t display_id) {
   }
 }
 
+display::ScreenBase* ScreenManagerStubInternal::GetScreen() {
+  return screen_.get();
+}
+
 }  // namespace display