Mac: Retain the child NSWindow in WidgetOwnerNSWindowAdapter before invoking close

ui/views/cocoa/native_widget_mac_nswindow.mm

 // Copyright 2014 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/native_widget_mac_nswindow.h"
 
 #include "base/mac/foundation_util.h"
 #import "ui/views/cocoa/bridged_native_widget.h"
 #import "ui/base/cocoa/user_interface_item_command_handler.h"
 #import "ui/views/cocoa/views_nswindow_delegate.h"
@@ skipping 27 matching lines @@
                               defer:(BOOL)deferCreation {
   if ((self = [super initWithContentRect:contentRect
                                styleMask:windowStyle
                                  backing:bufferingType
                                    defer:deferCreation])) {
     commandDispatcher_.reset([[CommandDispatcher alloc] initWithOwner:self]);
   }
   return self;
 }
 
+// This override doesn't do anything, but keeping it helps diagnose lifetime
+// issues in crash stacktraces by inserting a symbol on NativeWidgetMacNSWindow.
+- (void)dealloc {
+  [super dealloc];
+}
+
 // Public methods.
 
 - (void)setCommandDispatcherDelegate:(id<CommandDispatcherDelegate>)delegate {
   [commandDispatcher_ setDelegate:delegate];
 }
 
 // Private methods.
 
 - (ViewsNSWindowDelegate*)viewsNSWindowDelegate {
   return base::mac::ObjCCastStrict<ViewsNSWindowDelegate>([self delegate]);
@@ skipping 151 matching lines @@
     id appController = [NSApp delegate];
     DCHECK([appController
         conformsToProtocol:@protocol(NSUserInterfaceValidations)]);
     return [appController validateUserInterfaceItem:item];
   }
 
   return [super validateUserInterfaceItem:item];
 }
 
 @end