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

chrome/browser/ui/aura/native_window_tracker_aura.cc

-// 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.
-
-#include "chrome/browser/ui/aura/native_window_tracker_aura.h"
-
-#include "ui/aura/window.h"
-
-NativeWindowTrackerAura::NativeWindowTrackerAura(
-    gfx::NativeWindow window)
-    : window_(window) {
-  window->AddObserver(this);
-}
-
-NativeWindowTrackerAura::~NativeWindowTrackerAura() {
-  if (window_)
-    window_->RemoveObserver(this);
-}
-
-bool NativeWindowTrackerAura::WasNativeWindowClosed() const {
-  return window_ == nullptr;
-}
-
-void NativeWindowTrackerAura::OnWindowDestroying(
-    aura::Window* window) {
-  window_->RemoveObserver(this);
-  window_ = nullptr;
-}
-
-// static
-scoped_ptr<NativeWindowTracker> NativeWindowTracker::Create(
-    gfx::NativeWindow window) {
-  return scoped_ptr<NativeWindowTracker>(new NativeWindowTrackerAura(window));
-}