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

ui/views/widget/widget.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/widget/widget.h"
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 565 matching lines @@
 void Widget::Close() {
   if (widget_closed_) {
     // It appears we can hit this code path if you close a modal dialog then
     // close the last browser before the destructor is hit, which triggers
     // invoking Close again.
     return;
   }
 
   bool can_close = true;
   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
     // GTK tabbed panes and their children, so normal deregistration via

[sky, 2017/04/25 05:04:09]

This comment seems out of date.

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

I don't know what a GTK tabbed pane is, so I don't know how to update this
comment and/or remove the comment and/or code.

I believe FormManager was supposed to be FocusManager, so I fixed that.

     // |FormManager::ViewRemoved()| calls are fouled.  We clear focus here
     // to avoid these redundant steps and to avoid accessing deleted views
     // that may have been in focus.
     if (is_top_level() && focus_manager_.get())
       focus_manager_->SetFocusedView(NULL);
 
     for (WidgetObserver& observer : observers_)
       observer.OnWidgetClosing(this);
 
     native_widget_->Close();
-    widget_closed_ = true;
   }
 }
 
 void Widget::CloseNow() {
   for (WidgetObserver& observer : observers_)
     observer.OnWidgetClosing(this);
   native_widget_->CloseNow();
 }
 
 bool Widget::IsClosed() const {
@@ skipping 954 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // internal::NativeWidgetPrivate, NativeWidget implementation:
 
 internal::NativeWidgetPrivate* NativeWidgetPrivate::AsNativeWidgetPrivate() {
   return this;
 }
 
 }  // namespace internal
 }  // namespace views