Do not allow NULL to be passed into FocusManager::ViewRemoved.

ui/views/widget/widget.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/widget.h"
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 1050 matching lines @@
     focus_manager_.reset(FocusManagerFactory::Create(this, desktop_widget));
 
   native_widget_->InitModalType(widget_delegate_->GetModalType());
 
   FOR_EACH_OBSERVER(WidgetObserver, observers_, OnWidgetCreated(this));
 }
 
 void Widget::OnNativeWidgetDestroying() {
   // Tell the focus manager (if any) that root_view is being removed
   // in case that the focused view is under this root view.
-  if (GetFocusManager())
+  if (GetFocusManager() && root_view_)
     GetFocusManager()->ViewRemoved(root_view_.get());
   FOR_EACH_OBSERVER(WidgetObserver, observers_, OnWidgetDestroying(this));
   if (non_client_view_)
     non_client_view_->WindowClosing();
   widget_delegate_->WindowClosing();
 }
 
 void Widget::OnNativeWidgetDestroyed() {
   FOR_EACH_OBSERVER(WidgetObserver, observers_, OnWidgetDestroyed(this));
   widget_delegate_->DeleteDelegate();
@@ skipping 405 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // internal::NativeWidgetPrivate, NativeWidget implementation:
 
 internal::NativeWidgetPrivate* NativeWidgetPrivate::AsNativeWidgetPrivate() {
   return this;
 }
 
 }  // namespace internal
 }  // namespace views