Makes display roots be destroyed by client

services/ui/public/cpp/window_manager_delegate.h

Index: services/ui/public/cpp/window_manager_delegate.h
diff --git a/services/ui/public/cpp/window_manager_delegate.h b/services/ui/public/cpp/window_manager_delegate.h
index fe3b72bc9ac904f41dea75c05c1d6f33ce168ab2..67c79a62b6b18ab276272a989eb065ab56823ec8 100644
--- a/services/ui/public/cpp/window_manager_delegate.h
+++ b/services/ui/public/cpp/window_manager_delegate.h
@@ -106,6 +106,9 @@ class WindowManagerDelegate {
   virtual void OnWmNewDisplay(Window* window,
                               const display::Display& display) = 0;
 
+  // Called when a display is removed. |window| is the root of the display.
+  virtual void OnWmDisplayRemoved(Window* window) = 0;
+
   virtual mojom::EventResult OnAccelerator(uint32_t id, const ui::Event& event);
 
   virtual void OnWmPerformMoveLoop(