Switch pkg packages, pub, and dartdoc to use package: imports.

pkg/oauth2/test/credentials_test.dart

Index: pkg/oauth2/test/credentials_test.dart
diff --git a/pkg/oauth2/test/credentials_test.dart b/pkg/oauth2/test/credentials_test.dart
index e21b301c8922fd528269995e3e1d2f8bcd33993f..8e40a4a1709c9d254653a6888b87e58953c08d66 100644
--- a/pkg/oauth2/test/credentials_test.dart
+++ b/pkg/oauth2/test/credentials_test.dart
@@ -9,9 +9,10 @@ import 'dart:io';
 import 'dart:json' as JSON;
 import 'dart:uri';
 
-import '../../../pkg/unittest/lib/unittest.dart';
-import '../../../pkg/http/lib/http.dart' as http;
-import '../lib/oauth2.dart' as oauth2;
+import 'package:http/http.dart' as http;
+import 'package:oauth2/oauth2.dart' as oauth2;
+import 'package:unittest/unittest.dart';
+
 import 'utils.dart';
 
 final Uri tokenEndpoint = Uri.parse('http://example.com/token');