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

chrome/browser/ui/cocoa/browser_window_cocoa.h

Index: chrome/browser/ui/cocoa/browser_window_cocoa.h
diff --git a/chrome/browser/ui/cocoa/browser_window_cocoa.h b/chrome/browser/ui/cocoa/browser_window_cocoa.h
index a4f276f03feff57a3a79b0214231437acbbc5dce..350b9315ff97d233ae3855582187156c32a3b8ae 100644
--- a/chrome/browser/ui/cocoa/browser_window_cocoa.h
+++ b/chrome/browser/ui/cocoa/browser_window_cocoa.h
@@ -172,6 +172,9 @@ class BrowserWindowCocoa
   // 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_; }
 
@@ -199,6 +202,10 @@ class BrowserWindowCocoa
   // 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_