Start pulling pub from its own repo.

sdk/lib/_internal/pub/test/build/utils.dart

-// Copyright (c) 2013, 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.
-
-import 'dart:convert';
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-/// Runs the hosted test server and serves a valid "browser" package that
-/// contains the same files (but not their contents) as the real browser
-/// package.
-void serveBrowserPackage() {
-  serve([
-    d.dir('api', [
-      d.dir('packages', [
-        d.file('browser', JSON.encode({
-          'versions': [packageVersionApiMap(packageMap('browser', '1.0.0'))]
-        })),
-        d.dir('browser', [
-          d.dir('versions', [
-            d.file('1.0.0', JSON.encode(
-                packageVersionApiMap(
-                    packageMap('browser', '1.0.0'),
-                    full: true)))
-          ])
-        ])
-      ])
-    ]),
-    d.dir('packages', [
-      d.dir('browser', [
-        d.dir('versions', [
-          d.tar('1.0.0.tar.gz', [
-            d.file('pubspec.yaml', yaml(packageMap("browser", "1.0.0"))),
-            d.dir('lib', [
-              d.file('dart.js', 'contents of dart.js'),
-              d.file('interop.js', 'contents of interop.js')
-            ])
-          ])
-        ])
-      ])
-    ])
-  ]);
-}