Add a missing import to compile_platform_test.dart.

pkg/front_end/test/fasta/compile_platform_test.dart

 // Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
 library fasta.test.compile_platform_test;
 
+import 'dart:async';
 import 'dart:io';
 
 import 'package:async_helper/async_helper.dart';
 
 import 'package:expect/expect.dart';
 
 import '../../tool/_fasta/compile_platform.dart' show compilePlatform;
 
 main(List<String> arguments) async {
   await asyncTest(() async {
-    await withTemporyDirectory("compile_platform_test_", (Uri tmp) async {
+    await withTemporaryDirectory("compile_platform_test_", (Uri tmp) async {
       String patchedSdk = Uri.base
           .resolveUri(new Uri.file(Platform.resolvedExecutable))
           .resolve("patched_sdk")
           .toFilePath();
       // This first invocation should succeed.
       await compilePlatform(<String>[
         "-v",
         patchedSdk,
         tmp.resolve("platform.dill").toFilePath(),
         tmp.resolve("platform-outline.dill").toFilePath(),
@@ skipping 16 matching lines @@
         Expect.isTrue(
             e.startsWith("A member with disambiguated name '_withType' "));
         print("Failed as expected: $e");
         return;
       }
       Expect.fail("Test didn't throw expected exception.");
     });
   });
 }
 
-withTemporyDirectory(String prefix, Future f(Uri tmp)) async {
+withTemporaryDirectory(String prefix, Future f(Uri tmp)) async {
   Directory tmp = await Directory.systemTemp.createTemp(prefix);
   try {
     await f(tmp.uri);
   } finally {
     await tmp.delete(recursive: true);
   }
 }