Revert of Finish eliminating PlatformWindowMus

ui/views/mus/window_tree_host_mus.h

Index: ui/views/mus/window_tree_host_mus.h
diff --git a/ui/views/mus/window_tree_host_mus.h b/ui/views/mus/window_tree_host_mus.h
index e1930c341e9b304a932ce3a4bba173dee97b672c..30da7ed2d3fb0b6b0d99855d1ba1fb6128d281c9 100644
--- a/ui/views/mus/window_tree_host_mus.h
+++ b/ui/views/mus/window_tree_host_mus.h
@@ -11,20 +11,12 @@
 
 class SkBitmap;
 
-namespace bitmap_uploader {
- class BitmapUploader;
-}
-
 namespace mus {
 class Window;
 }
 
 namespace shell {
 class Connector;
-}
-
-namespace ui {
-class ViewProp;
 }
 
 namespace views {
@@ -40,6 +32,8 @@
                     mus::Window* window);
   ~WindowTreeHostMus() override;
 
+  PlatformWindowMus* platform_window();
+
  private:
   // aura::WindowTreeHostPlatform:
   void DispatchEvent(ui::Event* event) override;
@@ -50,10 +44,6 @@
   NativeWidgetMus* native_widget_;
   std::unique_ptr<InputMethodMUS> input_method_;
 
-  // Bitmap management.
-  std::unique_ptr<bitmap_uploader::BitmapUploader> bitmap_uploader_;
-  std::unique_ptr<ui::ViewProp> prop_;
-
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHostMus);
 };