Don't allow a widget to send close notifications more than once.

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 de3ac38f969274531808a3cbb822f406c27cf62d..aa128e585040ec6fc7c9000630f55aa50d059e8e 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -585,6 +585,9 @@ void Widget::Close() {
   if (non_client_view_)
     can_close = non_client_view_->CanClose();

[sky, 2017/04/25 05:04:10]

While you're here simplify this to an early return, e.g.

if (non_client_client_ && !non_client_view_->CanClose())
  return;

[Evan Stade, 2017/04/25 22:52:51]

Done.

   if (can_close) {
+    // The actions below can cause this function to be called again, so mark
+    // |this| as closed early. See crbug.com/714334
+    widget_closed_ = true;
     SaveWindowPlacement();
 
     // During tear-down the top-level focus manager becomes unavailable to
@@ -599,7 +602,6 @@ void Widget::Close() {
       observer.OnWidgetClosing(this);
 
     native_widget_->Close();
-    widget_closed_ = true;
   }
 }