Move remaining mus::WindowObserver lifecycle callbacks from PlatformWindowMus to NativeWidgetMus::M…

ui/views/mus/platform_window_mus.h

Index: ui/views/mus/platform_window_mus.h
diff --git a/ui/views/mus/platform_window_mus.h b/ui/views/mus/platform_window_mus.h
index 2ba86e59edcfaf6612099c8a3074ce3af99ca2f1..0553d3e4f1ae796fb94135532600d3d130ddee21 100644
--- a/ui/views/mus/platform_window_mus.h
+++ b/ui/views/mus/platform_window_mus.h
@@ -35,7 +35,6 @@ namespace views {
 // into views::NativeWidgetMus. See crbug.com/609555 for details.
 class VIEWS_MUS_EXPORT PlatformWindowMus
     : public NON_EXPORTED_BASE(ui::PlatformWindow),
-      public mus::WindowObserver,
       public NON_EXPORTED_BASE(mus::InputEventHandler) {
  public:
   PlatformWindowMus(ui::PlatformWindowDelegate* delegate,
@@ -64,12 +63,6 @@ class VIEWS_MUS_EXPORT PlatformWindowMus
  private:
   friend class PlatformWindowMusTest;
 
-  // mus::WindowObserver:
-  void OnWindowDestroyed(mus::Window* window) override;
-  void OnWindowFocusChanged(mus::Window* gained_focus,
-                            mus::Window* lost_focus) override;
-  void OnRequestClose(mus::Window* window) override;
-
   // mus::InputEventHandler:
   void OnWindowInputEvent(
       mus::Window* view,