Give all async exceptions in pub some sort of stack trace.

utils/tests/pub/test_pub.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.
 
 /**
  * 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.
  */
@@ skipping 830 matching lines @@
   Future _validateOneMatch(String dir, Future validate(String path)) {
     // Special-case strings to support multi-level names like "myapp/packages".
     if (name is String) {
       var path = join(dir, name);
       return exists(path).chain((exists) {
         if (!exists) Expect.fail('File $name in $dir not found.');
         return validate(path);
       });
     }
 
+    // TODO(nweiz): remove this when issue 4061 is fixed.
+    var stackTrace;
+    try {
+      throw null;
+    } catch (_, localStackTrace) {
+      stackTrace = localStackTrace;
+    }
+
     return listDir(dir).chain((files) {
       var matches = files.filter((file) => endsWithPattern(file, name));
       if (matches.length == 0) {
         Expect.fail('No files in $dir match pattern $name.');
       }
       if (matches.length == 1) return validate(matches[0]);
 
       var failures = [];
       var successes = 0;
       var completer = new Completer();
       checkComplete() {
         if (failures.length + successes != matches.length) return;
         if (successes > 0) {
           completer.complete(null);
           return;
         }
 
         var error = new StringBuffer();
         error.add("No files named $name in $dir were valid:\n");
         for (var failure in failures) {
           error.add("  ").add(failure).add("\n");
         }
-        completer.completeException(new ExpectException(error.toString()));
+        completer.completeException(
+            new ExpectException(error.toString()), stackTrace);
       }
 
       for (var match in matches) {
         var future = validate(match);
 
         future.handleException((e) {
           failures.add(e);
           checkComplete();
           return true;
         });
@@ skipping 644 matching lines @@
 /// calling [completion] is unnecessary.
 void expectLater(Future actual, matcher, {String reason,
     FailureHandler failureHandler, bool verbose: false}) {
   _schedule((_) {
     return actual.transform((value) {
       expect(value, matcher, reason: reason, failureHandler: failureHandler,
           verbose: false);
     });
   });
 }