Converts test_wm to use aura

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 478ce90f57494bb80a444a8afe5372f05a115dc1..fe00df0c1f332072552a61d637fd3075014b1541 100644
--- a/ui/aura/mus/window_manager_delegate.h
+++ b/ui/aura/mus/window_manager_delegate.h
@@ -110,8 +110,9 @@ 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;