[Mac] Inform reference counted objects that hold a weak Browser* when the Browser is being destroye…

chrome/browser/ui/cocoa/has_weak_browser_pointer.h

+// Copyright 2015 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_HAS_WEAK_BROWSER_POINTER_H_
+#define CHROME_BROWSER_UI_COCOA_HAS_WEAK_BROWSER_POINTER_H_
+
+// This allows reference counted objects holding a Browser* to be
+// notified that the Browser will be destroyed so they can invalidate their
+// Browser*, perform any necessary cleanup, and pass the notification onto any
+// objects they retain that also implement this protocol. This helps to prevent
+// use-after-free of Browser*, or anything else tied to the Browser's lifetime,
+// by objects that may be retained beyond the lifetime of their associated
+// Browser (e.g. NSViewControllers).
+@protocol HasWeakBrowserPointer
+@required
+// This is usually called by BrowserWindowController but can be called by any
+// object that's certain of Browser's destruction.
+- (void)browserWillBeDestroyed;
+@end
+
+#endif  // CHROME_BROWSER_UI_COCOA_HAS_WEAK_BROWSER_POINTER_H_