Refactor test servers to make them less global.

test/get/hosted/cached_pubspec_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.
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   integration('does not request a pubspec for a cached package', () {
     servePackages((builder) => builder.serve("foo", "1.2.3"));
 
     d.appDir({"foo": "1.2.3"}).create();
 
     // Get once so it gets cached.
     pubGet();
 
     // Clear the cache. We don't care about anything that was served during
     // the initial get.
-    getRequestedPaths();
+    globalServer.clearRequestedPaths();
 
     d.cacheDir({"foo": "1.2.3"}).validate();
     d.packagesDir({"foo": "1.2.3"}).validate();
 
     // Run the solver again now that it's cached.
     pubGet();
 
     // The get should not have requested the pubspec since it's local already.
-    getRequestedPaths().then((paths) {
+    globalServer.requestedPaths.then((paths) {
       expect(paths, isNot(contains("packages/foo/versions/1.2.3.yaml")));
     });
   });
 }