mus: Changes SetDisplayRoot() to create actual display

services/ui/display/screen_manager_stub_internal.h

Index: services/ui/display/screen_manager_stub_internal.h
diff --git a/services/ui/display/screen_manager_stub_internal.h b/services/ui/display/screen_manager_stub_internal.h
index bca5ab986ee0b1354742782ecabdd7eca7232f08..ea68fa1e80f204a3153dceb1bb5e08b03e6c6c44 100644
--- a/services/ui/display/screen_manager_stub_internal.h
+++ b/services/ui/display/screen_manager_stub_internal.h
@@ -13,6 +13,8 @@
 
 namespace display {
 
+class ScreenBase;
+
 // ScreenManagerStubInternal provides the necessary functionality to configure a
 // fixed 1024x768 display for non-ozone platforms.
 class ScreenManagerStubInternal : public ScreenManager {
@@ -28,12 +30,15 @@ class ScreenManagerStubInternal : public ScreenManager {
   void AddInterfaces(service_manager::BinderRegistry* registry) override;
   void Init(ScreenManagerDelegate* delegate) override;
   void RequestCloseDisplay(int64_t display_id) override;
+  display::ScreenBase* GetScreen() override;
 
   // Sample display information.
   Display display_;
 
   ScreenManagerDelegate* delegate_ = nullptr;
 
+  std::unique_ptr<ScreenBase> screen_;
+
   base::WeakPtrFactory<ScreenManagerStubInternal> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenManagerStubInternal);