Web.PublishedCache - introduce contextual caches

src/Umbraco.Web/PublishedCache/ContextualPublishedCache.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Umbraco.Core.Models;
+
+namespace Umbraco.Web.PublishedCache
+{
+    /// <summary>
+    /// Provides access to cached contents in a specified context.
+    /// </summary>
+    internal abstract class ContextualPublishedCache
+    {
+        protected readonly UmbracoContext UmbracoContext;
+
+        protected ContextualPublishedCache(UmbracoContext umbracoContext)
+        {
+            UmbracoContext = umbracoContext;
+        }
+
+        /// <summary>
+        /// Gets a content identified by its unique identifier.
+        /// </summary>
+        /// <param name="contentId">The content unique identifier.</param>
+        /// <returns>The content, or null.</returns>
+        public abstract IPublishedContent GetById(int contentId);
+
+        /// <summary>
+        /// Gets contents at root.
+        /// </summary>
+        /// <returns>The contents.</returns>
+        public abstract IEnumerable<IPublishedContent> GetAtRoot();
+
+        /// <summary>
+        /// Gets a content resulting from an XPath query.
+        /// </summary>
+        /// <param name="xpath">The XPath query.</param>
+        /// <param name="vars">Optional XPath variables.</param>
+        /// <returns>The content, or null.</returns>
+        public abstract IPublishedContent GetSingleByXPath(string xpath, Core.Xml.XPathVariable[] vars);
+
+        /// <summary>
+        /// Gets contents resulting from an XPath query.
+        /// </summary>
+        /// <param name="xpath">The XPath query.</param>
+        /// <param name="vars">Optional XPath variables.</param>
+        /// <returns>The contents.</returns>
+        public abstract IEnumerable<IPublishedContent> GetByXPath(string xpath, Core.Xml.XPathVariable[] vars);
+    }
+}