Do not allow NULL to be passed into FocusManager::ViewRemoved.

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index 3de91f7b5175a13237f5df26fd6a347ebc3a6b1d..62b4b56680940483f338c2a56a1222da3279f264 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -1068,7 +1068,7 @@ void Widget::OnNativeWidgetCreated(bool desktop_widget) {
 void Widget::OnNativeWidgetDestroying() {
   // Tell the focus manager (if any) that root_view is being removed
   // in case that the focused view is under this root view.
-  if (GetFocusManager())
+  if (GetFocusManager() && root_view_)
     GetFocusManager()->ViewRemoved(root_view_.get());
   FOR_EACH_OBSERVER(WidgetObserver, observers_, OnWidgetDestroying(this));
   if (non_client_view_)