Address a crash under -[NSWindow close] via a WeakPtr PostTask from Browser::TabStripEmpty()

chrome/browser/ui/cocoa/browser_window_cocoa.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_BROWSER_WINDOW_COCOA_H_
 #define CHROME_BROWSER_UI_COCOA_BROWSER_WINDOW_COCOA_H_
 
 #include "base/mac/scoped_nsobject.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/extensions/extension_keybinding_registry.h"
@@ skipping 154 matching lines @@
                     const SearchModel::State& new_state) override;
 
   // Adds the given FindBar cocoa controller to this browser window.
   void AddFindBar(FindBarCocoaController* find_bar_cocoa_controller);
 
   // Updates the window's alert state. If the new alert state is
   // TabAlertState::AUDIO_PLAYING or TabAlertState::AUDIO_MUTING then sets
   // the window's title to reflect that.
   void UpdateAlertState(TabAlertState alert_state);
 
+  // Called when the controller's window invokes -windowWillClose:.
+  void OnWindowWillClose();
+
   // Returns the cocoa-world BrowserWindowController
   BrowserWindowController* cocoa_controller() { return controller_; }
 
   // Returns window title based on the active tab title and the window's alert
   // state.
   NSString* WindowTitle();
 
   // Returns the current alert state, determined by the alert state of tabs. Set
   // by UpdateAlertState.
   TabAlertState alert_state() { return alert_state_; }
 
  protected:
   void DestroyBrowser() override;
 
  private:
   NSWindow* window() const;  // Accessor for the (current) |NSWindow|.
 
   Browser* browser_;  // weak, owned by controller
   BrowserWindowController* controller_;  // weak, owns us
   base::scoped_nsobject<NSString> pending_window_title_;
   ui::WindowShowState initial_show_state_;
   NSInteger attention_request_id_;  // identifier from requestUserAttention
 
   // Preserves window alert state to show appropriate icon in the window title
   // which can be audio playing, muting or none (determined by alert state of
   // tabs.
   TabAlertState alert_state_;
+
+  // True when the controlled window invokes -windowWillClose:, and it may no
+  // longer be safe to access [controller_ window].
+  bool window_closed_;
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_BROWSER_WINDOW_COCOA_H_