Nukes aura::WindowDestructionObserver. It's effectively the same as

content/browser/renderer_host/render_widget_host_view_aura.cc

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_widget_host_view_aura.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 36 matching lines @@
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/client/cursor_client_observer.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/client/stacking_client.h"
 #include "ui/aura/client/tooltip_client.h"
 #include "ui/aura/client/window_types.h"
 #include "ui/aura/env.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/window.h"
-#include "ui/aura/window_destruction_observer.h"
 #include "ui/aura/window_observer.h"
 #include "ui/aura/window_tracker.h"
 #include "ui/base/clipboard/scoped_clipboard_writer.h"
 #include "ui/base/events/event.h"
 #include "ui/base/events/event_utils.h"
 #include "ui/base/gestures/gesture_recognizer.h"
 #include "ui/base/hit_test.h"
 #include "ui/base/ime/input_method.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/compositor/layer.h"
@@ skipping 2401 matching lines @@
       return;
   }
 
   // We need to handle the Escape key for Pepper Flash.
   if (is_fullscreen_ && event->key_code() == ui::VKEY_ESCAPE) {
     // Focus the window we were created from.
     if (host_tracker_.get() && !host_tracker_->windows().empty()) {
       aura::Window* host = *(host_tracker_->windows().begin());
       aura::client::FocusClient* client = aura::client::GetFocusClient(host);
       if (client) {
-        // Calling host->Focus() may delete |this|. We create a local
-        // observer for that. In that case we exit without further
-        // access to any members.
-        aura::WindowDestructionObserver destruction_observer(window_);
+        // Calling host->Focus() may delete |this|. We create a local observer
+        // for that. In that case we exit without further access to any members.
+        aura::WindowTracker tracker;
+        aura::Window* window = window_;
+        tracker.Add(window);
         host->Focus();
-        if (destruction_observer.destroyed()) {
+        if (!tracker.Contains(window)) {
           event->SetHandled();
           return;
         }
       }
     }
     if (!in_shutdown_) {
       in_shutdown_ = true;
       host_->Shutdown();
     }
   } else {
@@ skipping 713 matching lines @@
     RenderWidgetHost* widget) {
   return new RenderWidgetHostViewAura(widget);
 }
 
 // static
 void RenderWidgetHostViewPort::GetDefaultScreenInfo(WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }
 
 }  // namespace content