Emit OnNativeWidgetDestroying() before clearing the NSWindowDelegate.

ui/views/widget/native_widget_mac.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.
 
 #include "ui/views/widget/native_widget_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include <utility>
 
@@ skipping 88 matching lines @@
   return GetWidget()->widget_delegate()->GetModalType() ==
          ui::MODAL_TYPE_WINDOW;
 }
 
 void NativeWidgetMac::OnWindowWillClose() {
   // Note: If closed via CloseNow(), |bridge_| will already be reset. If closed
   // by the user, or via Close() and a RunLoop, notify observers while |bridge_|
   // is still a valid pointer, then reset it.
   if (bridge_) {
     delegate_->OnNativeWidgetDestroying();
+    [GetNativeWindow() setDelegate:nil];
     bridge_.reset();
   }
   delegate_->OnNativeWidgetDestroyed();
   if (ownership_ == Widget::InitParams::NATIVE_WIDGET_OWNS_WIDGET)
     delete this;
 }
 
 int NativeWidgetMac::SheetPositionY() {
   NSView* view = GetNativeView();
   return
@@ skipping 643 matching lines @@
   [[ViewsNSWindowCloseAnimator alloc] initWithWindow:window];
 }
 
 - (void)animationDidEnd:(NSAnimation*)animation {
   [window_ close];
   [animation_ setDelegate:nil];
   [self release];
 }
 
 @end