Merge the dart:uri library into dart:core and update the Uri class

pkg/oauth2/lib/src/handle_access_token_response.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;
 
 import 'dart:io';
 import 'dart:json' as JSON;
-import 'dart:uri';
 
 import 'package:http/http.dart' as http;
 
 import 'credentials.dart';
 import 'authorization_exception.dart';
 
 /// The amount of time, in seconds, to add as a "grace period" for credential
 /// expiration. This allows credential expiration checks to remain valid for a
 /// reasonable amount of time.
 const _EXPIRATION_GRACE = 10;
@@ skipping 116 matching lines @@
 
 void _validate(
     http.Response response,
     Uri tokenEndpoint,
     bool condition,
     String message) {
   if (condition) return;
   throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
       '$message.\n\n${response.body}');
 }