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

ui/views/focus/focus_manager.cc

Index: ui/views/focus/focus_manager.cc
diff --git a/ui/views/focus/focus_manager.cc b/ui/views/focus/focus_manager.cc
index bd6b0dc19fe4749a958afe41f8c49dd158ed446a..80a4dc8d6bdd0c7b67ee984e6081e434cebe6db1 100644
--- a/ui/views/focus/focus_manager.cc
+++ b/ui/views/focus/focus_manager.cc
@@ -517,7 +517,8 @@ void FocusManager::ViewRemoved(View* removed) {
   // clear the focus.  However, it's not safe to call ClearFocus()
   // (and in turn ClearNativeFocus()) here because ViewRemoved() can
   // be called while the top level widget is being destroyed.
-  if (focused_view_ && removed->Contains(focused_view_))
+  DCHECK(removed);
+  if (removed->Contains(focused_view_))
     SetFocusedView(NULL);
 }