Fix crash when closing a constrained window in win aura. The crash happens because the aura::Window…

ui/views/widget/native_widget_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/native_widget_aura.h"
 
 #include "base/bind.h"
 #include "base/string_util.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/activation_client.h"
@@ skipping 841 matching lines @@
     // focus and doesn't expect a blur).  OnBlur() shouldn't be called during
     // destruction unless WIDGET_OWNS_NATIVE_WIDGET is set (which is just the
     // case in tests).
     if (!destroying_) {
       if (GetWidget()->GetInputMethod())
         GetWidget()->GetInputMethod()->OnBlur();
     } else {
       DCHECK_EQ(ownership_, Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET);
     }
 
-    delegate_->OnNativeBlur(
-        aura::client::GetFocusClient(window_)->GetFocusedWindow());
+    aura::client::FocusClient* client = aura::client::GetFocusClient(window_);
+    if (client)  // NULL during destruction of aura::Window.
+      delegate_->OnNativeBlur(client->GetFocusedWindow());
   }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // NativeWidgetAura, aura::WindowDragDropDelegate implementation:
 
 void NativeWidgetAura::OnDragEntered(const ui::DropTargetEvent& event) {
   DCHECK(drop_helper_.get() != NULL);
   last_drop_operation_ = drop_helper_->OnDragOver(event.data(),
       event.location(), event.source_operations());
@@ skipping 180 matching lines @@
   return aura::Env::GetInstance()->is_mouse_button_down();
 }
 
 // static
 bool NativeWidgetPrivate::IsTouchDown() {
   return aura::Env::GetInstance()->is_touch_down();
 }
 
 }  // namespace internal
 }  // namespace views