Fix bug in doWhile where it completes an error synchronously with an error.

sdk/lib/async/future.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.
 
 part of dart.async;
 
 /// A type representing values that are either `Future<T>` or `T`.
 ///
 /// This class declaration is a public stand-in for an internal
 /// future-or-value generic type. References to this class are resolved to the
@@ skipping 467 matching lines @@
     _Future doneSignal = new _Future();
     var nextIteration;
     // Bind this callback explicitly so that each iteration isn't bound in the
     // context of all the previous iterations' callbacks.
     nextIteration = Zone.current.bindUnaryCallback((bool keepGoing) {
       if (keepGoing) {
         FutureOr<bool> result;
         try {
           result = f();
         } catch (error, stackTrace) {
-          _completeWithErrorCallback(doneSignal, error, stackTrace);
+          // Cannot use _completeWithErrorCallback because it completes
+          // the future synchronously.
+          _asyncCompleteWithErrorCallback(doneSignal, error, stackTrace);
           return;
         }
         if (result is Future<bool>) {
           result.then(nextIteration, onError: doneSignal._completeError);
           return;
         }
         nextIteration(result);
       } else {
         doneSignal._complete(null);
       }
@@ skipping 367 matching lines @@
 // for error replacement first.
 void _completeWithErrorCallback(_Future result, error, stackTrace) {
   AsyncError replacement = Zone.current.errorCallback(error, stackTrace);
   if (replacement != null) {
     error = _nonNullError(replacement.error);
     stackTrace = replacement.stackTrace;
   }
   result._completeError(error, stackTrace);
 }
 
+// Like [_completeWIthErrorCallback] but completes asynchronously.

[eernst, 2017/04/06 11:45:57]

Typo: `WIth` --> `With`.

+void _asyncCompleteWithErrorCallback(_Future result, error, stackTrace) {
+  AsyncError replacement = Zone.current.errorCallback(error, stackTrace);
+  if (replacement != null) {
+    error = _nonNullError(replacement.error);
+    stackTrace = replacement.stackTrace;
+  }
+  result._asyncCompleteError(error, stackTrace);
+}
+
 /** Helper function that converts `null` to a [NullThrownError]. */
 Object _nonNullError(Object error) => error ?? new NullThrownError();