Mac: Retain the child NSWindow in WidgetOwnerNSWindowAdapter before invoking close

ui/views/cocoa/widget_owner_nswindow_adapter.mm

 // Copyright 2015 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.
 
 #import "ui/views/cocoa/widget_owner_nswindow_adapter.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/logging.h"
 #include "base/mac/sdk_forward_declarations.h"
@@ skipping 44 matching lines @@
   DCHECK(anchor_window_);
 
   [[NSNotificationCenter defaultCenter]
       addObserver:observer_bridge_
          selector:@selector(windowWillClose:)
              name:NSWindowWillCloseNotification
            object:anchor_window_];
 }
 
 void WidgetOwnerNSWindowAdapter::OnWindowWillClose() {
-  [child_->ns_window() close];
+  // Retain the child window before closing it. If the last reference to the
+  // NSWindow goes away inside -[NSWindow close], then bad stuff can happen.
+  // See e.g. http://crbug.com/616701.
+  base::scoped_nsobject<NSWindow> child_window(child_->ns_window(),
+                                               base::scoped_policy::RETAIN);
+
+  // AppKit child window relationships break when the windows are not visible,
+  // so if the child is not visible, it won't currently be a child.
+  DCHECK(![child_window isVisible] || [child_window parentWindow]);
+  DCHECK([child_window delegate]);
+
+  [child_window close];
   // Note: |this| will be deleted here.
+
+  DCHECK(![child_window parentWindow]);
+  DCHECK(![child_window delegate]);
 }
 
 NSWindow* WidgetOwnerNSWindowAdapter::GetNSWindow() {
   return anchor_window_;
 }
 
 gfx::Vector2d WidgetOwnerNSWindowAdapter::GetChildWindowOffset() const {
   NSRect rect_in_window =
       [anchor_view_ convertRect:[anchor_view_ bounds] toView:nil];
   NSRect rect_in_screen = [anchor_window_ convertRectToScreen:rect_in_window];
@@ skipping 12 matching lines @@
   DCHECK_EQ(child, child_);
   [GetNSWindow() removeChildWindow:child->ns_window()];
   delete this;
 }
 
 WidgetOwnerNSWindowAdapter::~WidgetOwnerNSWindowAdapter() {
   [[NSNotificationCenter defaultCenter] removeObserver:observer_bridge_];
 }
 
 }  // namespace views