Properly report errors with no stack traces when not using --trace.

sdk/lib/_internal/pub/lib/src/utils.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.
 
 /// Generic utility functions. Stuff that should possibly be in core.
 library pub.utils;
 
 import 'dart:async';
 import "dart:collection";
 import "dart:convert";
@@ skipping 99 matching lines @@
       }
       completer.completeError(e, stackTrace);
     });
   };
 
   if (captureStackChains) {
     Chain.capture(wrappedCallback, onError: completer.completeError);
   } else {
     runZoned(wrappedCallback, onError: (e, stackTrace) {
       if (stackTrace == null) {
+        stackTrace = new Chain.current();
+      } else {
         stackTrace = new Chain([new Trace.from(stackTrace)]);
-      } else {
-        stackTrace = new Chain([]);
       }
       completer.completeError(e, stackTrace);
     });
   }
 
   return completer.future;
 }
 
 /// Returns a [StreamTransformer] that will call [onDone] when the stream
 /// completes.
@@ skipping 728 matching lines @@
     error is AnalyzerErrorGroup ||
     error is IsolateSpawnException ||
     error is FileSystemException ||
     error is HttpException ||
     error is http.ClientException ||
     error is OSError ||
     error is ProcessException ||
     error is SocketException ||
     error is WebSocketException;
 }