cros: Adds ShellPort functions for simplified display mode

ash/mus/bridge/shell_port_mash.h

Index: ash/mus/bridge/shell_port_mash.h
diff --git a/ash/mus/bridge/shell_port_mash.h b/ash/mus/bridge/shell_port_mash.h
index ac839c83bb264e4082ef92c12c1848bf9ecb210e..14bfc1a91dddc104c3428beaad293a60f19a76ef 100644
--- a/ash/mus/bridge/shell_port_mash.h
+++ b/ash/mus/bridge/shell_port_mash.h
@@ -104,8 +104,12 @@ class ShellPortMash : public ShellPort {
   void SetLaserPointerEnabled(bool enabled) override;
   void SetPartialMagnifierEnabled(bool enabled) override;
   void CreatePointerWatcherAdapter() override;
+  AshWindowTreeHost* CreateAshWindowTreeHost(
+      const AshWindowTreeHostInitParams& init_params) override;
   void CreatePrimaryHost() override;
   void InitHosts(const ShellInitParams& init_params) override;
+  std::unique_ptr<display::NativeDisplayDelegate> CreateNativeDisplayDelegate()
+      override;
   std::unique_ptr<AcceleratorController> CreateAcceleratorController() override;
 
  private: