Stop working around issue 2644.

pkg/oauth2/lib/src/utils.dart

Index: pkg/oauth2/lib/src/utils.dart
diff --git a/pkg/oauth2/lib/src/utils.dart b/pkg/oauth2/lib/src/utils.dart
index d0e5f114e7d6e8b7232e2e4faab58a2c5639f001..759357e78f28bd3caeeef3e40dc5450b196158a3 100644
--- a/pkg/oauth2/lib/src/utils.dart
+++ b/pkg/oauth2/lib/src/utils.dart
@@ -13,7 +13,7 @@ import "package:crypto/crypto.dart";
 /// parameters if a name conflict occurs.
 Uri addQueryParameters(Uri url, Map<String, String> parameters) {
   var queryMap = queryToMap(url.query);
-  mapAddAll(queryMap, parameters);
+  queryMap.addAll(parameters);
   return url.resolve("?${mapToQuery(queryMap)}");
 }
 
@@ -47,11 +47,6 @@ String mapToQuery(Map<String, String> map) {
   }).join("&");
 }
 
-/// Add all key/value pairs from [source] to [destination], overwriting any
-/// pre-existing values.
-void mapAddAll(Map destination, Map source) =>
-  source.forEach((key, value) => destination[key] = value);
-
 /// Decode a URL-encoded string. Unlike [Uri.decodeComponent], this includes
 /// replacing `+` with ` `.
 String urlDecode(String encoded) =>