Make OnWmDisplayRemoved() take a WindowTreeHost

ui/aura/mus/window_manager_delegate.h

Index: ui/aura/mus/window_manager_delegate.h
diff --git a/ui/aura/mus/window_manager_delegate.h b/ui/aura/mus/window_manager_delegate.h
index b8adfc85e8a876fc54de3f6fe7b5cb596ce2cb81..fe8203e83630f9d32f9031ae5bd9d7456c7d6df5 100644
--- a/ui/aura/mus/window_manager_delegate.h
+++ b/ui/aura/mus/window_manager_delegate.h
@@ -113,8 +113,9 @@ class AURA_EXPORT WindowManagerDelegate {
       std::unique_ptr<WindowTreeHostMus> window_tree_host,
       const display::Display& display) = 0;
 
-  // Called when a display is removed. |window| is the root of the display.
-  virtual void OnWmDisplayRemoved(Window* window) = 0;
+  // Called when a display is removed. |window_tree_host| is the WindowTreeHost
+  // for the display.
+  virtual void OnWmDisplayRemoved(WindowTreeHostMus* window_tree_host) = 0;
 
   // Called when a display is modified.
   virtual void OnWmDisplayModified(const display::Display& display) = 0;