Avoid network requests while resolving versions when possible.

sdk/lib/_internal/pub/test/test_pub.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.
 
 /// Test infrastructure for testing pub. Unlike typical unit tests, most pub
 /// tests are integration tests that stage some stuff on the file system, run
 /// pub, and then validate the results. This library provides an API to build
 /// tests like that.
 library test_pub;
 
@@ skipping 70 matching lines @@
 /// A future that will complete to the port used for the current server.
 Future<int> get port => _portCompleter.future;
 
 /// Gets the list of paths that have been requested from the server since the
 /// last time this was called (or since the server was first spun up).
 Future<List<String>> getRequestedPaths() {
   return schedule(() {
     var paths = _requestedPaths.toList();
     _requestedPaths.clear();
     return paths;
-  });
+  }, "get previous network requests");
 }
 
 /// Creates an HTTP server to serve [contents] as static files. This server will
 /// exist only for the duration of the pub run.
 ///
 /// Subsequent calls to [serve] will replace the previous server.
 void serve([List<d.Descriptor> contents]) {
   var baseDir = d.dir("serve-dir", contents);
 
   _hasServer = true;
@@ skipping 740 matching lines @@
   bool matches(item, Map matchState) {
     if (item is! Pair) return false;
     return _firstMatcher.matches(item.first, matchState) &&
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }