Microsoft.Windows.Themes程序集在哪里

我在XAML中编写了一个用户控件，在它被编译成C#后，生成的C#有以下行：

using Microsoft.Windows.Themes;

现在抛出一个错误：

命名空间中不存在类型或命名空间名称"Themes"Microsoft.Windows"（是否缺少程序集引用？）

我想既然我不能影响编译后的C#的输出（没有什么可从XAML中删除的），我只会将其添加为引用。

但是，"添加引用"对话框不包含Microsoft.Windows.Themes。这不是.NET的一部分吗？

以下是导致此问题的XAML用户控件示例：

<UserControl x:Class="GG.UserControls.MainMenu"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <StackPanel>
        <Menu VerticalAlignment="Top" Background="{x:Null}">
            ... // Just static menu items.
        </Menu>
    </StackPanel>
</UserControl>

背后的C#代码：

using System;
using System.Windows.Controls;
namespace GG.UserControls
{
    /// <summary>
    /// Interaction logic for MainMenu.xaml
    /// </summary>
    public partial class MainMenu : UserControl
    {
        public MainMenu()
        {
            InitializeComponent();
        }
    }
}

下面是一个编译的C#示例：

#pragma checksum "..'..'..'..'UserControls'MainMenu.xaml" "{406ea660-64cf-4c82-b6f0-42d48172a799}" "5A85C5B16565514165AD23641F944BC6"
//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.17020
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------
using GG;
using GG.UserControls;
using Microsoft.Windows.Shell;
using Microsoft.Windows.Themes; // <---- WTF?
using System;
using System.Diagnostics;
using System.Windows;
using System.Windows.Automation;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Markup;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Media.Effects;
using System.Windows.Media.Imaging;
using System.Windows.Media.Media3D;
using System.Windows.Media.TextFormatting;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Shell;

namespace GG.UserControls {

    /// <summary>
    /// ChangesetHistory
    /// </summary>
    public partial class MainMenu : System.Windows.Controls.UserControl, System.Windows.Markup.IComponentConnector {
        private bool _contentLoaded;
        /// <summary>
        /// InitializeComponent
        /// </summary>
        [System.Diagnostics.DebuggerNonUserCodeAttribute()]
        [System.CodeDom.Compiler.GeneratedCodeAttribute("PresentationBuildTasks", "4.0.0.0")]
        public void InitializeComponent() {
            if (_contentLoaded) {
                return;
            }
            _contentLoaded = true;
            System.Uri resourceLocater = new System.Uri("/GG;component/usercontrols/mainmenu.xaml", System.UriKind.Relative);
            #line 1 "..'..'..'..'UserControls'MainMenu.xaml"
            System.Windows.Application.LoadComponent(this, resourceLocater);
            #line default
            #line hidden
        }
        [System.Diagnostics.DebuggerNonUserCodeAttribute()]
        [System.CodeDom.Compiler.GeneratedCodeAttribute("PresentationBuildTasks", "4.0.0.0")]
        [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
        [System.Diagnostics.CodeAnalysis.SuppressMessageAttribute("Microsoft.Design", "CA1033:InterfaceMethodsShouldBeCallableByChildTypes")]
        [System.Diagnostics.CodeAnalysis.SuppressMessageAttribute("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity")]
        [System.Diagnostics.CodeAnalysis.SuppressMessageAttribute("Microsoft.Performance", "CA1800:DoNotCastUnnecessarily")]
        void System.Windows.Markup.IComponentConnector.Connect(int connectionId, object target) {
            this._contentLoaded = true;
        }
    }
}