Don't decodeHttpEntityString on urlencoded post data.

sdk/lib/io/http_body_impl.dart

Index: sdk/lib/io/http_body_impl.dart
diff --git a/sdk/lib/io/http_body_impl.dart b/sdk/lib/io/http_body_impl.dart
index c8d90d7eef647bd1077b1a8a8f30021b2bd4a8ca..900dff51e9304d8349993e36a0972c2b38ad8584 100644
--- a/sdk/lib/io/http_body_impl.dart
+++ b/sdk/lib/io/http_body_impl.dart
@@ -123,11 +123,8 @@ class _HttpBodyHandler {
                   var map = _HttpUtils.splitQueryString(
                       body.body, encoding: defaultEncoding);
                   var result = {};
-                  String parse(String s) {
-                    return _HttpUtils.decodeHttpEntityString(s);
-                  }
                   for (var key in map.keys) {
-                    result[parse(key)] = parse(map[key]);
+                    result[key] = map[key];
                   }
                   return new _HttpBody(contentType, "form", result);
                 });