Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Xml/System/Xml/XmlUrlResolverAsync.cs

@@ -0,0 +1,21 @@
+
+using System.Runtime.Versioning;
+using System.Threading.Tasks;
+
+namespace System.Xml
+{
+    public partial class XmlUrlResolver : XmlResolver {
+
+        // Maps a URI to an Object containing the actual resource.
+        [ResourceConsumption(ResourceScope.Machine)]
+        [ResourceExposure(ResourceScope.Machine)]
+        public override async Task<Object> GetEntityAsync(Uri absoluteUri, string role, Type ofObjectToReturn) {
+            if (ofObjectToReturn == null || ofObjectToReturn == typeof(System.IO.Stream) || ofObjectToReturn == typeof(System.Object)) {
+                return await DownloadManager.GetStreamAsync(absoluteUri, _credentials, _proxy, _cachePolicy).ConfigureAwait(false);
+            }
+            else {
+                throw new XmlException(Res.Xml_UnsupportedClass, string.Empty);
+            }
+        }
+    }
+}