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

chrome/browser/ui/native_window_tracker.h

Index: chrome/browser/ui/native_window_tracker.h
diff --git a/chrome/browser/ui/native_window_tracker.h b/chrome/browser/ui/native_window_tracker.h
new file mode 100644
index 0000000000000000000000000000000000000000..c08dc126546b766861acc8cecc5d0097a5f93d28
--- /dev/null
+++ b/chrome/browser/ui/native_window_tracker.h
@@ -0,0 +1,22 @@
+// 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_NATIVE_WINDOW_TRACKER_H_
+#define CHROME_BROWSER_UI_NATIVE_WINDOW_TRACKER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "ui/gfx/native_widget_types.h"
+
+// An observer which detects when a gfx::NativeWindow is closed.
+class NativeWindowTracker {
+ public:
+  virtual ~NativeWindowTracker() {}
+
+  static scoped_ptr<NativeWindowTracker> Create(gfx::NativeWindow window);
+
+  // Returns true if the native window passed to Create() has been closed.
+  virtual bool WasNativeWindowClosed() const = 0;
+};
+
+#endif  // CHROME_BROWSER_UI_NATIVE_WINDOW_TRACKER_H_