update download progress reporting

MediaBrowser.Controller/IO/StreamHelper.cs

@@ -1,6 +1,7 @@
 using System.IO;
 using System.Threading;
 using System;
+using System.Threading.Tasks;
 
 namespace MediaBrowser.Controller.IO
 {
@@ -23,5 +24,27 @@ namespace MediaBrowser.Controller.IO
                 }
             }
         }
+
+        public static async Task CopyToAsync(Stream source, Stream destination, int bufferSize, IProgress<double> progress, long contentLength, CancellationToken cancellationToken)
+        {
+            byte[] buffer = new byte[bufferSize];
+            int read;
+            long totalRead = 0;
+
+            while ((read = source.Read(buffer, 0, buffer.Length)) != 0)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+
+                destination.Write(buffer, 0, read);
+
+                totalRead += read;
+
+                double pct = totalRead;
+                pct /= contentLength;
+                pct *= 100;
+
+                progress.Report(pct);
+            }
+        }
     }
 }