Mark the classes as serializable to match the inband framework

Author: lanlanlee2008

src/OutputCacheModuleAsync/CachedVary.cs

@@ -1,6 +1,7 @@
 namespace Microsoft.AspNet.OutputCache {
     using System;
 
+    [Serializable]
     sealed class CachedVary {
         public string[] ContentEncodings { get; set; }
         public string[] Headers { get; set; }

src/OutputCacheModuleAsync/HttpCachePolicySettings.cs

@@ -4,6 +4,7 @@
     using System.Web;
     using System.Linq;
 
+    [Serializable]
     sealed class HttpCachePolicySettings {
         public HttpCacheability Cacheability { get; set; }
         public IEnumerable<KeyValuePair<HttpCacheValidateHandler, object>> ValidationCallbackInfo { get; set; }

src/OutputCacheModuleAsync/OutputCacheEntry.cs

@@ -3,6 +3,7 @@
     using System.Collections;
     using System.Collections.Specialized;
 
+    [Serializable]
     sealed class OutputCacheEntry {
         public Guid CachedVaryId { get; set; }
         public HttpCachePolicySettings Settings { get; set; }