The lost EPiServer.TypedPageBase<PageData>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using EPiServer.Core;
using EPiServer.Web.PageExtensions;

namespace EPiServer
{
    /// <summary>
    /// Page Template class for supporting strongly typed PageData objects with an arbitrary type <typeparamref name="TPageData"/>.
    /// </summary>
    /// <typeparam name="TPageData">The strongly typed PageData type.</typeparam>
    public class TypedPageBase<TPageData> : PageBase
        where TPageData : PageData, new()
    {
        /// <summary>
        /// Creates a new instance of <see cref="TypedPageBase"/> with a default set of features enabled.
        /// </summary>
        public TypedPageBase() : this(
            SiteRedirect.OptionFlag | 
            ContextMenu.OptionFlag | 
            PageStatistics.OptionFlag | 
            SaveCurrentPage.OptionFlag, 0) { }

        /// <summary>
        /// Creates a new instance of <see cref="TypedPageBase"/> where individual features can be enabled and disabled.
        /// </summary>
        /// <param name="enable">The bitmask for enabling certain features.</param>
        /// <param name="disable">The bitmask for disabling certain features.</param>
        public TypedPageBase(int enable, int disable) : base(enable, disable) { }

        private TPageData _currentPage;
        /// <summary>
        /// Gets a strongly typed PageData of type <typeparamref name="TPageData"/>.
        /// </summary>
        public virtual TPageData CurrentTypedPage
        {
            get
            {
                if (_currentPage == null)
                {
                    _currentPage = PageData.ShallowCopy<TPageData>(base.CurrentPage);
                }
                return _currentPage;
            }
        }
    }
}

    /// <summary>
    /// A base class for page template implementations.
    /// </summary>
    /// <typeparam name="TPageData">A PageData class that will represent the content class for the page template.</typeparam>
    public class PageBase<TPageData> : EPiServer.PageBase
        where TPageData : EPiServer.Core.PageData, new ()
    {
        private TPageData _currentPage;
        /// <summary>
        /// Creates an instance of the PageBase type.
        /// </summary>
        public PageBase() : 
                this((EPiServer.Web.PageExtensions.SiteRedirect.OptionFlag 
                                | (EPiServer.Web.PageExtensions.ContextMenu.OptionFlag 
                                | (EPiServer.Web.PageExtensions.PageStatistics.OptionFlag | EPiServer.Web.PageExtensions.SaveCurrentPage.OptionFlag))), 0)
        {
        }
        /// <summary>
        /// Creates an instance of the PageBase type with specified page feature configuration.
        /// </summary>
        /// <param name="enable">The page options to enable.</param>
        /// <param name="disable">The page options to disable.</param>
        public PageBase(int enable, int disable) : 
                base(enable, disable)
        {
        }
        /// <summary>
        /// Gets page data for the current page.
        /// </summary>
        public new virtual TPageData CurrentPage
        {
            get
            {
                if ((this._currentPage == null))
                {
                    this._currentPage = EPiServer.Core.PageData.ShallowCopy<TPageData>(base.CurrentPage);
                }
                return this._currentPage;
            }
        }
    }