Reduce creation of ViewsDelegate

ui/views/test/test_views_delegate.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/test/test_views_delegate.h"
 
 #include "ui/wm/core/wm_state.h"
 
 
 namespace views {
 
 TestViewsDelegate::TestViewsDelegate()
     : use_transparent_windows_(false) {
   DCHECK(!ViewsDelegate::views_delegate);
   ViewsDelegate::views_delegate = this;
   wm_state_.reset(new wm::WMState);
 }
 
 TestViewsDelegate::~TestViewsDelegate() {
-  ViewsDelegate::views_delegate = NULL;
+  if (ViewsDelegate::views_delegate == this)
+    ViewsDelegate::views_delegate = NULL;
 }
 
 void TestViewsDelegate::SetUseTransparentWindows(bool transparent) {
   use_transparent_windows_ = transparent;
 }
 
 void TestViewsDelegate::OnBeforeWidgetInit(
     Widget::InitParams* params,
     internal::NativeWidgetDelegate* delegate) {
   if (params->opacity == Widget::InitParams::INFER_OPACITY) {
     params->opacity = use_transparent_windows_ ?
         Widget::InitParams::TRANSLUCENT_WINDOW :
         Widget::InitParams::OPAQUE_WINDOW;
   }
 }
 
 }  // namespace views