Fix OAuth2 tests, and disable them on non-dart:io platforms.

pkg/oauth2/test/handle_access_token_response_test.dart

 // 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.
 
 library handle_access_token_response_test;
 
 import 'dart:io';
 import 'dart:json';
 import 'dart:uri';
 
 import '../../unittest/lib/unittest.dart';
 import '../../http/lib/http.dart' as http;
 import '../lib/oauth2.dart' as oauth2;
 import '../lib/src/handle_access_token_response.dart';
 import 'utils.dart';
 
 final Uri tokenEndpoint = new Uri.fromString("https://example.com/token");
 
 final Date startTime = new Date.now();
 
-Credentials handle(http.Response response) =>
+oauth2.Credentials handle(http.Response response) =>
   handleAccessTokenResponse(response, tokenEndpoint, startTime, ["scope"]);
 
 void main() {
   group('an error response', () {
     oauth2.Credentials handleError(
         {String body: '{"error": "invalid_request"}',
          int statusCode: 400,
          Map<String, String> headers:
              const {"content-type": "application/json"}}) =>
       handle(new http.Response(body, statusCode, headers: headers));
@@ skipping 63 matching lines @@
       expect(() => handleError(body: JSON.stringify({
         "error": "invalid_request",
         "error_uri": "http://example.com/error"
       })), throwsAuthorizationException);
     });
   });
 
   group('a success response', () {
     oauth2.Credentials handleSuccess(
         {String contentType: "application/json",
-         String accessToken: 'access token',
-         String tokenType: 'bearer',
-         String expiresIn,
-         String refreshToken,
-         String scope}) {
+         accessToken: 'access token',
+         tokenType: 'bearer',
+         expiresIn,
+         refreshToken,
+         scope}) {
       return handle(new http.Response(JSON.stringify({
         'access_token': accessToken,
         'token_type': tokenType,
         'expires_in': expiresIn,
         'refresh_token': refreshToken,
         'scope': scope
       }), 200, headers: {'content-type': contentType}));
     }
 
     test('returns the correct credentials', () {
@@ skipping 62 matching lines @@
     test('with a non-string scope throws a FormatException', () {
       expect(() => handleSuccess(scope: 12), throwsFormatException);
     });
 
     test('with a scope sets the scopes', () {
       var credentials = handleSuccess(scope: "scope1 scope2");
       expect(credentials.scopes, equals(["scope1", "scope2"]));
     });
   });
 }