Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/serve/web_socket/path_to_urls_errors_test.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS d.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 file.
-
-library pub_tests;
-
-import 'package:json_rpc_2/error_code.dart' as rpc_error_code;
-import 'package:path/path.dart' as p;
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-import '../utils.dart';
-
-main() {
-  // TODO(rnystrom): Split into independent tests.
-  initConfig();
-  integration("pathToUrls errors on bad inputs", () {
-    d.dir(
-        "foo",
-        [
-            d.libPubspec("foo", "1.0.0"),
-            d.dir("web", [d.file("foo.txt", "foo")])]).create();
-
-    d.dir(appPath, [d.appPubspec({
-        "foo": {
-          "path": "../foo"
-        }
-      }),
-          d.file("top-level.txt", "top-level"),
-          d.dir("bin", [d.file("foo.txt", "foo"),]),
-          d.dir("lib", [d.file("myapp.dart", "myapp"),])]).create();
-
-    pubServe(shouldGetFirst: true);
-
-    // Bad arguments.
-    expectWebSocketError("pathToUrls", {
-      "path": 123
-    },
-        rpc_error_code.INVALID_PARAMS,
-        'Parameter "path" for method "pathToUrls" must be a string, but was ' '123.');
-
-    expectWebSocketError("pathToUrls", {
-      "path": "main.dart",
-      "line": 12.34
-    },
-        rpc_error_code.INVALID_PARAMS,
-        'Parameter "line" for method "pathToUrls" must be an integer, but was '
-            '12.34.');
-
-    // Unserved directories.
-    expectNotServed(p.join('bin', 'foo.txt'));
-    expectNotServed(p.join('nope', 'foo.txt'));
-    expectNotServed(p.join("..", "bar", "lib", "bar.txt"));
-    expectNotServed(p.join("..", "foo", "web", "foo.txt"));
-
-    endPubServe();
-  });
-}
-
-void expectNotServed(String path) {
-  expectWebSocketError("pathToUrls", {
-    "path": path
-  }, NOT_SERVED, 'Asset path "$path" is not currently being served.');
-}