Add debugging info to a failing case in the pub tests.

sdk/lib/_internal/pub/lib/src/http.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.
 
 /// Helpers for dealing with HTTP.
 library pub.http;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
@@ skipping 81 matching lines @@
             error.osError.errorCode == -2 ||
             error.osError.errorCode == -5 ||
             error.osError.errorCode == 11001 ||
             error.osError.errorCode == 11004) {
           fail('Could not resolve URL "${request.url.origin}".');
         } else if (error.osError.errorCode == -12276) {
           fail('Unable to validate SSL certificate for '
               '"${request.url.origin}".');
         }
       }
+      print('Error in PubHttpClient.send (issue 12581) error: $error');
+      print('    stacktrace: $stackTrace');
       throw error;
     }), HTTP_TIMEOUT, 'fetching URL "${request.url}"');
   }
 
   /// Logs the fact that [request] was sent, and information about it.
   void _logRequest(http.BaseRequest request) {
     var requestLog = new StringBuffer();
     requestLog.writeln("HTTP ${request.method} ${request.url}");
     request.headers.forEach((name, value) =>
         requestLog.writeln(_logField(name, value)));
@@ skipping 105 matching lines @@
 
 /// Exception thrown when an HTTP operation fails.
 class PubHttpException implements Exception {
   final http.Response response;
 
   const PubHttpException(this.response);
 
   String toString() => 'HTTP error ${response.statusCode}: '
       '${response.reasonPhrase}';
 }