Notify WidgetRemovalsObserver when RootView is removed

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 1353 matching lines @@
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // Widget, protected:
 
 internal::RootView* Widget::CreateRootView() {
   return new internal::RootView(this);
 }
 
 void Widget::DestroyRootView() {
+  NotifyWillRemoveView(root_view_.get());
   non_client_view_ = NULL;
   root_view_.reset();
 }
 
 void Widget::OnDragWillStart() {}
 
 void Widget::OnDragComplete() {}
 
 ////////////////////////////////////////////////////////////////////////////////
 // Widget, private:
@@ skipping 109 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // internal::NativeWidgetPrivate, NativeWidget implementation:
 
 internal::NativeWidgetPrivate* NativeWidgetPrivate::AsNativeWidgetPrivate() {
   return this;
 }
 
 }  // namespace internal
 }  // namespace views