cros: Adds ShellPort functions for simplified display mode

ash/host/ash_window_tree_host.cc

Index: ash/host/ash_window_tree_host.cc
diff --git a/ash/host/ash_window_tree_host.cc b/ash/host/ash_window_tree_host.cc
index 939f097d35648af36c2c33d1b4c972f8e1cb175b..d2afd91ca48cd5511fd55a0bc82dc399d1549b8e 100644
--- a/ash/host/ash_window_tree_host.cc
+++ b/ash/host/ash_window_tree_host.cc
@@ -6,6 +6,7 @@
 
 #include "ash/host/ash_window_tree_host_init_params.h"
 #include "ash/host/ash_window_tree_host_unified.h"
+#include "ash/shell_port.h"
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/events/event.h"
@@ -49,6 +50,11 @@ void AshWindowTreeHost::TranslateLocatedEvent(ui::LocatedEvent* event) {
 // static
 AshWindowTreeHost* AshWindowTreeHost::Create(
     const AshWindowTreeHostInitParams& init_params) {
+  AshWindowTreeHost* ash_window_tree_host =
+      ShellPort::Get()->CreateAshWindowTreeHost(init_params);
+  if (ash_window_tree_host)
+    return ash_window_tree_host;
+
   if (init_params.offscreen)
     return new AshWindowTreeHostUnified(init_params.initial_bounds);
 #if defined(USE_OZONE)