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

sdk/lib/_internal/dartdoc/bin/dartdoc.dart

Index: sdk/lib/_internal/dartdoc/bin/dartdoc.dart
diff --git a/sdk/lib/_internal/dartdoc/bin/dartdoc.dart b/sdk/lib/_internal/dartdoc/bin/dartdoc.dart
index 3c906bfc98d840a58eb3ba701faa1111fb566122..c84c72c7d717860bab8bcfdefa2974ed9e990cac 100644
--- a/sdk/lib/_internal/dartdoc/bin/dartdoc.dart
+++ b/sdk/lib/_internal/dartdoc/bin/dartdoc.dart
@@ -19,11 +19,10 @@ library dartdoc;
 import 'dart:async';
 import 'dart:io';
 
-import '../lib/dartdoc.dart';
-
 // TODO(rnystrom): Use "package:" URL (#4968).
-import '../../../../../pkg/args/lib/args.dart';
-import '../../../../../pkg/pathos/lib/path.dart' as path;
+import '../lib/dartdoc.dart';
+import 'package:args/args.dart';
+import 'package:pathos/path.dart' as path;
 
 /**
  * Run this from the `lib/_internal/dartdoc` directory.