Fix a crash in DesktopNativeWidgetHelperAura when closing tabs because it was dereferncing a delete…

ui/views/widget/desktop_native_widget_helper_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 "ui/views/widget/desktop_native_widget_helper_aura.h"
 
 #include "ui/aura/client/dispatcher_client.h"
 #include "ui/aura/desktop/desktop_activation_client.h"
 #include "ui/aura/desktop/desktop_cursor_client.h"
 #include "ui/aura/desktop/desktop_dispatcher_client.h"
@@ skipping 154 matching lines @@
       widget_->GetWidget()));
   ui::HWNDSubclass::AddFilterToTarget(root_window_->GetAcceleratedWidget(),
                                       hwnd_message_filter_.get());
 #endif
 }
 
 aura::RootWindow* DesktopNativeWidgetHelperAura::GetRootWindow() {
   return root_window_.get();
 }
 
+void DesktopNativeWidgetHelperAura::OnWindowDestroying(aura::Window* window) {
+  window_->RemoveObserver(this);
+  window_ = NULL;
+}
+
 gfx::Rect DesktopNativeWidgetHelperAura::ModifyAndSetBounds(
     const gfx::Rect& bounds) {
   gfx::Rect out_bounds = bounds;
   if (root_window_.get() && !out_bounds.IsEmpty()) {
     // TODO(scottmg): This avoids the AdjustWindowRect that ash wants to
     // adjust the top level on Windows.
 #if !defined(OS_WIN)
     root_window_->SetHostBounds(out_bounds);
 #endif
     out_bounds.set_x(0);
@@ skipping 43 matching lines @@
   widget_->GetWidget()->Close();
 }
 
 void DesktopNativeWidgetHelperAura::OnRootWindowMoved(
     const aura::RootWindow* root,
     const gfx::Point& new_origin) {
   widget_->GetWidget()->OnNativeWidgetMove();
 }
 
 }  // namespace views