Cache version list results even when they fail.

sdk/lib/_internal/pub/test/hosted/version_negotiation_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.
 
 library pub_tests;
 
 import 'package:scheduled_test/scheduled_server.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:shelf/shelf.dart' as shelf;
 
@@ skipping 37 matching lines @@
             "url": server.url.then((url) => url.toString())
           }
         }
       }).create();
 
       var pub = startPub(args: [command.name]);
 
       server.handle('GET', '/api/packages/foo',
           (request) => new shelf.Response(406));
 
-      // TODO(nweiz): this shouldn't request the versions twice (issue 11077).
-      server.handle('GET', '/api/packages/foo',
-          (request) => new shelf.Response(406));
-
       pub.shouldExit(1);
 
       pub.stderr.expect(emitsLines(
           "Pub 0.1.2+3 is incompatible with the current version of localhost.\n"
           "Upgrade pub to the latest version and try again."));
     });
   });
 }