Make Name and FileName getters lazy

It seems like both the Name and FileName does
quite a bit of work in their getters. Let's
fetch them lazily instead.

Author: khellang

src/Microsoft.AspNet.Http/Features/FormFile.cs

@@ -4,21 +4,24 @@
 using System.IO;
 using Microsoft.AspNet.Http.Internal;
 using Microsoft.Net.Http.Headers;
+using static Microsoft.Net.Http.Headers.HeaderUtilities;
 
 namespace Microsoft.AspNet.Http.Features.Internal
 {
     public class FormFile : IFormFile
     {
         private readonly Stream _baseStream;
         private readonly long _baseStreamOffset;
+        private readonly ContentDispositionHeaderValue _contentDisposition;
+        private string _name;
+        private string _fileName;
 
         public FormFile(Stream baseStream, long baseStreamOffset, long length, ContentDispositionHeaderValue contentDisposition)
         {
             _baseStream = baseStream;
             _baseStreamOffset = baseStreamOffset;
+            _contentDisposition = contentDisposition;
             Length = length;
-            Name = HeaderUtilities.RemoveQuotes(contentDisposition.Name) ?? string.Empty;
-            FileName = HeaderUtilities.RemoveQuotes(contentDisposition.FileName) ?? string.Empty;
         }
 
         public string ContentDisposition
@@ -37,9 +40,9 @@ public string ContentType
 
         public long Length { get; }
 
-        public string Name { get; }
+        public string Name => _name ?? (_name = RemoveQuotes(_contentDisposition.Name) ?? string.Empty);
 
-        public string FileName { get; }
+        public string FileName => _fileName ?? (_fileName = RemoveQuotes(_contentDisposition.FileName) ?? string.Empty);
 
         public Stream OpenReadStream()
         {