[dart2js] Missed file clamped to 2.10

Change-Id: I7eb820d6326572c106633a2632d77e22bcff7ae7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240740
Reviewed-by: Joshua Litt <joshualitt@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

pkg/compiler/test/end_to_end/trim_component_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.10
+
 import 'package:expect/expect.dart';
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/binary/ast_from_binary.dart' show BinaryBuilder;