Removed MediaFileSystemExtensions and just added the methods to the MediaFileSystem which are more discoverable.

Added Code Annotations to all file system classes pointing to the new #U4-1156 tracking item to publicize.

src/Umbraco.Core/IO/MediaFileSystem.cs

@@ -1,5 +1,9 @@
-using System.Linq;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
 using System.Text;
+using Umbraco.Core.CodeAnnotations;
+using Umbraco.Core.Configuration;
 
 namespace Umbraco.Core.IO
 {
@@ -7,11 +11,47 @@ namespace Umbraco.Core.IO
 	/// A custom file system provider for media
 	/// </summary>
 	[FileSystemProvider("media")]
+	[UmbracoExperimentalFeature("http://issues.umbraco.org/issue/U4-1156", "Will be declared public after 4.10")]
 	internal class MediaFileSystem : FileSystemWrapper
 	{
 		public MediaFileSystem(IFileSystem wrapped)
 			: base(wrapped)
 		{
 		}
+
+		public string GetRelativePath(int propertyId, string fileName)
+		{
+			var seperator = UmbracoSettings.UploadAllowDirectories
+				? Path.DirectorySeparatorChar
+				: '-';
+
+			return propertyId.ToString() + seperator + fileName;
+		}
+
+		public IEnumerable<string> GetThumbnails(string path)
+		{
+			var parentDirectory = System.IO.Path.GetDirectoryName(path);
+			var extension = System.IO.Path.GetExtension(path);
+
+			return GetFiles(parentDirectory)
+				.Where(x => x.StartsWith(path.TrimEnd(extension) + "_thumb"))
+				.ToList();
+		}
+
+		public void DeleteFile(string path, bool deleteThumbnails)
+		{
+			DeleteFile(path);
+
+			if (!deleteThumbnails)
+				return;
+
+			DeleteThumbnails(path);
+		}
+
+		public void DeleteThumbnails(string path)
+		{
+			GetThumbnails(path)
+				.ForEach(DeleteFile);
+		}
 	}
 }