Emit OnNativeWidgetDestroying() before clearing the NSWindowDelegate.

ui/views/cocoa/bridged_native_widget.h

 // 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.
 
 #ifndef UI_VIEWS_COCOA_BRIDGED_NATIVE_WIDGET_H_
 #define UI_VIEWS_COCOA_BRIDGED_NATIVE_WIDGET_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include <memory>
@@ skipping 303 matching lines @@
   // shadow needs to be invalidated when a frame is received for the new shape.
   bool invalidate_shadow_on_frame_swap_ = false;
 
   // Whether the window's visibility is suppressed currently. For opaque non-
   // modal windows, the window's alpha value is set to 0, till the frame from
   // the compositor arrives to avoid "blinking".
   bool initial_visibility_suppressed_ = false;
 
   AssociatedViews associated_views_;
 
+  // We will set this flag to false inside OnWindowWillClose().
+  // For teardown flows (e.g. Widget::WIDGET_OWNS_NATIVE_WIDGET or
+  // Widget::CloseNow()) we needs to be invoked manually OnWindowWillClose()
+  // in destructor.
+  // But [NSWindow close] would synchronously call OnWindowWillClose() so to
+  // prevent second call in destructor we use this flag.
+  bool close_window_ = true;
+
   DISALLOW_COPY_AND_ASSIGN(BridgedNativeWidget);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_COCOA_BRIDGED_NATIVE_WIDGET_H_