[benchmark] Cleanup lint violations

Fix violations of lints that I expect have no influence on the
performance characteristics of this benchmark:

* directives_ordering

Change-Id: I3aa77c9351507a54dfb1b5e3a8295cea3fc66540
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/433269
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Ömer Ağacan <omersa@google.com>

benchmarks/WasmDataTransfer/dart/WasmDataTransfer.dart

@@ -2,8 +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.
 
-import 'dart:js_interop';
 import 'dart:convert';
+import 'dart:js_interop';
 import 'dart:typed_data';
 
 import 'package:benchmark_harness/benchmark_harness.dart';
@@ -76,7 +76,7 @@ class WasmDataTransferFromBrowserString extends Benchmark {
     // But currently we use internal one/two byte strings and using string
     // interpolation forces transfer of string to be internal string.
     //
-    // Though string interpolation also causes other work (it convers JS string
+    // Though string interpolation also causes other work (it converts JS string
     // to dart and then allocates new string for interpolation result)
     use('a${jsonString.toDart}');
   }