Fix several problems with offline mode.

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 200 matching lines @@
         });
       }, 'localhost', 0).then((server) {
         _server = server;
         _portCompleter.complete(_server.port);
         currentSchedule.onComplete.schedule(_closeServer);
       });
     });
   }, 'starting a server serving:\n${baseDir.describe()}');
 }
 
+/// Like [serve], but reports an error if a request ever comes in to the server.
+void serveErrors() {
+  _hasServer = true;
+
+  schedule(() async {
+    await _closeServer();
+
+    _server = await shelf_io.serve((request) {
+      fail("The HTTP server received an unexpected request:\n"
+          "${request.method} ${request.requestedUri}");
+      return new shelf.Response.forbidden(null);
+    }, 'localhost', 0);
+
+    _portCompleter.complete(_server.port);
+    currentSchedule.onComplete.schedule(_closeServer);
+  });
+}
+
 /// Closes [_server].
 ///
 /// Returns a [Future] that completes after the [_server] is closed.
 Future _closeServer() {
   if (_server == null) return new Future.value();
   var future = _server.close();
   _server = null;
   _hasServer = false;
   _portCompleterCache = null;
   return future;
@@ skipping 742 matching lines @@
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     return description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }
 
 /// A [StreamMatcher] that matches multiple lines of output.
 StreamMatcher emitsLines(String output) => inOrder(output.split("\n"));