mus: Changes SetDisplayRoot() to create actual display

services/ui/service.h

Index: services/ui/service.h
diff --git a/services/ui/service.h b/services/ui/service.h
index 92e5f6078282a3680bd217cbe7214221b5345007..9d88bfd0cfb05330635dcb99a8e1a7925891cb2a 100644
--- a/services/ui/service.h
+++ b/services/ui/service.h
@@ -83,6 +83,20 @@ class Service
   ~Service() override;
 
  private:
+  // How the ScreenManager is configured.
+  enum ScreenManagerConfig {
+    // Initial state.
+    UNKNOWN,
+
+    // ScreenManager runs locally.
+    INTERNAL,
+
+    // Used when the window manager supplies a value of false for
+    // |automatically_create_display_roots|. In this config the ScreenManager
+    // is configured to forward calls.
+    FORWARDING,
+  };
+
   // Holds InterfaceRequests received before the first WindowTreeHost Display
   // has been established.
   struct PendingRequest;
@@ -111,6 +125,8 @@ class Service
   void OnFirstDisplayReady() override;
   void OnNoMoreDisplays() override;
   bool IsTestConfig() const override;
+  void OnWillCreateTreeForWindowManager(
+      bool automatically_create_display_roots) override;
 
   // service_manager::InterfaceFactory<mojom::AccessibilityManager>
   // implementation.
@@ -198,6 +214,10 @@ class Service
 
   service_manager::BinderRegistry registry_;
 
+  // Set to true in StartDisplayInit().
+  bool is_gpu_ready_ = false;
+  ScreenManagerConfig screen_manager_config_ = ScreenManagerConfig::UNKNOWN;
+
   DISALLOW_COPY_AND_ASSIGN(Service);
 };