Revert of Finish eliminating PlatformWindowMus

ash/host/ash_window_tree_host_unified.cc

Index: ash/host/ash_window_tree_host_unified.cc
diff --git a/ash/host/ash_window_tree_host_unified.cc b/ash/host/ash_window_tree_host_unified.cc
index ea96b99f88a79e8811ca3fde9472411f49647241..7f6869b498b7162c232a92eda26c8eac6b0c7daf 100644
--- a/ash/host/ash_window_tree_host_unified.cc
+++ b/ash/host/ash_window_tree_host_unified.cc
@@ -15,7 +15,6 @@
 #include "ui/aura/window_targeter.h"
 #include "ui/compositor/compositor.h"
 #include "ui/gfx/geometry/insets.h"
-#include "ui/gfx/native_widget_types.h"
 #include "ui/platform_window/stub/stub_window.h"
 
 namespace ash {
@@ -51,8 +50,7 @@
 AshWindowTreeHostUnified::AshWindowTreeHostUnified(
     const gfx::Rect& initial_bounds)
     : AshWindowTreeHostPlatform() {
-  std::unique_ptr<ui::PlatformWindow> window(
-      new ui::StubWindow(this, gfx::kNullAcceleratedWidget));
+  std::unique_ptr<ui::PlatformWindow> window(new ui::StubWindow(this));
   window->SetBounds(initial_bounds);
   SetPlatformWindow(std::move(window));
 }