Makes display roots be destroyed by client

services/ui/ws/window_tree.h

Index: services/ui/ws/window_tree.h
diff --git a/services/ui/ws/window_tree.h b/services/ui/ws/window_tree.h
index 2a59479ba98d19e6bb548eab2812d3b74b2c578b..245d0c68cba755c3478ed4392f4668c66e8ef137 100644
--- a/services/ui/ws/window_tree.h
+++ b/services/ui/ws/window_tree.h
@@ -167,6 +167,7 @@ class WindowTree : public mojom::WindowTree,
                  const ClientWindowId& child_id);
   bool AddTransientWindow(const ClientWindowId& window_id,
                           const ClientWindowId& transient_window_id);
+  bool DeleteWindow(const ClientWindowId& window_id);
   bool SetModal(const ClientWindowId& window_id);
   std::vector<const ServerWindow*> GetWindowTree(
       const ClientWindowId& window_id) const;
@@ -193,6 +194,10 @@ class WindowTree : public mojom::WindowTree,
                      const ui::Event& event,
                      bool needs_ack);
 
+  // Called when a display has been removed. This is only called on the
+  // WindowTree associated with a WindowManager.
+  void OnDisplayDestroying(int64_t display_id);
+
   // Called when |tree|'s jankiness changes (see janky_ for definition).
   // Notifies the window manager client so it can update UI for the affected
   // window(s).