Mark oauth2 as running outside of dart:io contexts.

pkg/pkg.status

 # Copyright (c) 2012, 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 file.
 
 # Don't run any test-like files that show up in packages directories. It
 # shouldn't be necessary to run "pub install" in these packages, but if you do
 # it shouldn't break the tests.
 */packages/*/*: Skip
 */*/packages/*/*: Skip
 */*/*/packages/*/*: Skip
@@ skipping 192 matching lines @@
 http/test/io/*: Fail, OK # Uses dart:io.
 http_parser/test/web_socket_test: Fail, OK # Uses dart:io
 http_server/test/*: Fail, OK # Uses dart:io.
 intl/test/date_time_format_file_even_test: Fail, OK # Uses dart:io.
 intl/test/date_time_format_file_odd_test: Fail, OK # Uses dart:io.
 intl/test/find_default_locale_standalone_test: Fail, OK # Uses dart:io.
 intl/test/message_extraction/examples_parsing_test: Fail, OK # Users dart:io
 intl/test/message_extraction/failed_extraction_test: Fail, OK # Users dart:io
 intl/test/message_extraction/message_extraction_test: Fail, OK # Uses dart:io.
 intl/test/message_extraction/really_fail_extraction_test: Fail, OK # Users dart:io
-oauth2/test/authorization_code_grant_test: Fail, OK # Uses dart:io.
-oauth2/test/client_test: Fail, OK # Uses dart:io.
-oauth2/test/credentials_test: Fail, OK # Uses dart:io.
-oauth2/test/handle_access_token_response_test: Fail, OK # Uses dart:io.
 observe/test/transformer_test: Fail, OK # Uses dart:io.
 path/test/io_test: Fail, OK # Uses dart:io.
 polymer/test/build/*: Fail, OK # Uses dart:io.
 shelf/test/shelf_io_test: Fail, OK # Uses dart:io
 smoke/test/codegen/end_to_end_test: Skip # Uses dart:io.
 smoke/test/codegen/recorder_test: Skip # Uses dart:io.
 third_party/angular_tests/browser_test/core_dom/cookies: Fail # Issue 16337
 third_party/angular_tests/vm_test: Skip # Uses dart:io
 watcher/test/*: Fail, OK # Uses dart:io.
 
@@ skipping 114 matching lines @@
 third_party/angular_tests/browser_test/change_detection/dirty_checking_change_detector: Skip # Issue 17152
 
 [ $use_repository_packages ]
 analyzer/test/*: PubGetError
 
 [ $runtime == ie9 ]
 polymer: Pass, Fail, Timeout # Issue 16717
 
 [ $runtime == drt ]
 http/test/html/client_test: Skip # Issue 18566