Fixes possible crash in ~Display

services/ui/ws/window_manager_state.cc

Index: services/ui/ws/window_manager_state.cc
diff --git a/services/ui/ws/window_manager_state.cc b/services/ui/ws/window_manager_state.cc
index 93b3d3cde76d15cbce86a6f860f7faea12770a9f..68454b4cdd514a8ff4432edc8cc6c3e2686a77e4 100644
--- a/services/ui/ws/window_manager_state.cc
+++ b/services/ui/ws/window_manager_state.cc
@@ -119,6 +119,9 @@ WindowManagerState::WindowManagerState(WindowTree* window_tree)
 }
 
 WindowManagerState::~WindowManagerState() {
+  for (auto& display_root : window_manager_display_roots_)
+    display_root->display()->OnWillDestroyTree(window_tree_);
+
   for (auto& display_root : orphaned_window_manager_display_roots_)
     display_root->root()->RemoveObserver(this);
 }