Make sure Future.forEach properly pipes exceptions.

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 [Future] represents a delayed computation. It is used to obtain a not-yet
  * available value, or error, sometime in the future.  Receivers of a
  * [Future] can register callbacks that handle the value or error once it is
@@ skipping 172 matching lines @@
    * completes when all elements have been processed.
    *
    * The return values of all [Future]s are discarded. Any errors will cause the
    * iteration to stop and will be piped through the returned [Future].
    */
   static Future forEach(Iterable input, Future f(element)) {
     _FutureImpl doneSignal = new _FutureImpl();
     Iterator iterator = input.iterator;
     void nextElement(_) {
       if (iterator.moveNext()) {
-        f(iterator.current).then(nextElement, onError: doneSignal._setError);
+        new Future.of(() => f(iterator.current))
+            .then(nextElement, onError: doneSignal._setError);
       } else {
         doneSignal._setValue(null);
       }
     }
     nextElement(null);
     return doneSignal;
   }
 
   /**
    * When this future completes with a value, then [onValue] is called with this
@@ skipping 152 matching lines @@
    * The argument [exception] should not be `null`.
    *
    * If [exception] is an [AsyncError], it is used directly as the error
    * message sent to the future's listeners, and [stackTrace] is ignored.
    *
    * Otherwise the [exception] and an optional [stackTrace] is combined into an
    * [AsyncError] and sent to this future's listeners.
    */
   void completeError(Object exception, [Object stackTrace]);
 }