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

sdk/lib/_internal/pub/lib/src/utils.dart

Index: sdk/lib/_internal/pub/lib/src/utils.dart
diff --git a/sdk/lib/_internal/pub/lib/src/utils.dart b/sdk/lib/_internal/pub/lib/src/utils.dart
index 2dec8034a8d580f9781d881d826303751189d21e..d9ab8a95294d54646db34daaf44d38ba1bcee9cc 100644
--- a/sdk/lib/_internal/pub/lib/src/utils.dart
+++ b/sdk/lib/_internal/pub/lib/src/utils.dart
@@ -117,9 +117,9 @@ Future captureErrors(Future callback(), {bool captureStackChains: false}) {
   } else {
     runZoned(wrappedCallback, onError: (e, stackTrace) {
       if (stackTrace == null) {
-        stackTrace = new Chain([new Trace.from(stackTrace)]);
+        stackTrace = new Chain.current();
       } else {
-        stackTrace = new Chain([]);
+        stackTrace = new Chain([new Trace.from(stackTrace)]);
       }
       completer.completeError(e, stackTrace);
     });