Fix crash when user closes window prior to the "Confirm Install" prompt showing

chrome/browser/ui/aura/native_window_deletion_observer_aura.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 CHROME_BROWSER_UI_AURA_NATIVE_WINDOW_DELETION_OBSERVER_AURA_H_
+#define CHROME_BROWSER_UI_AURA_NATIVE_WINDOW_DELETION_OBSERVER_AURA_H_
+
+#include "chrome/browser/ui/native_window_deletion_observer.h"
+#include "ui/aura/window_observer.h"
+
+class NativeWindowDeletionObserverAura : public NativeWindowDeletionObserver,
+                                         public aura::WindowObserver {
+ public:
+  explicit NativeWindowDeletionObserverAura(gfx::NativeWindow window);
+  ~NativeWindowDeletionObserverAura() override;
+
+  // NativeWindowDeletionObserver:
+  bool IsNativeWindowAlive() const override;
+
+ private:
+  // aura::WindowObserver:
+  void OnWindowDestroying(aura::Window* window) override;
+
+  aura::Window* window_;
+
+  DISALLOW_COPY_AND_ASSIGN(NativeWindowDeletionObserverAura);
+};
+
+#endif  // CHROME_BROWSER_UI_AURA_NATIVE_WINDOW_DELETION_OBSERVER_AURA_H_