Let completers complete in the zone they were constructed in.

sdk/lib/async/future_impl.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;
 
 deprecatedFutureValue(_FutureImpl future) =>
   future._isComplete ? future._resultOrListeners : null;
 
 abstract class _Completer<T> implements Completer<T> {
   final Future<T> future;
   bool _isComplete = false;
 
   _Completer() : future = new _FutureImpl<T>() {
     _FutureImpl futureImpl = future;
     futureImpl._zone.expectCallback();
   }
 
   void _setFutureValue(T value);
   void _setFutureError(error);
 
   void complete([T value]) {
     if (_isComplete) throw new StateError("Future already completed");
     _isComplete = true;
     _FutureImpl futureImpl = future;
-    futureImpl._zone.cancelCallbackExpectation();
     _setFutureValue(value);
   }
 
   void completeError(Object error, [Object stackTrace = null]) {
     if (_isComplete) throw new StateError("Future already completed");
     _isComplete = true;
     if (stackTrace != null) {
       // Force the stack trace onto the error, even if it already had one.
       _attachStackTrace(error, stackTrace);
     }
     _FutureImpl futureImpl = future;
-    if (futureImpl._inSameErrorZone(_Zone.current)) {
-      futureImpl._zone.cancelCallbackExpectation();
-      _setFutureError(error);
-    } else {
-      _Zone.current.handleUncaughtError(error);
-    }
+    _setFutureError(error);
   }
 
   bool get isCompleted => _isComplete;
 }
 
 class _AsyncCompleter<T> extends _Completer<T> {
   void _setFutureValue(T value) {
     _FutureImpl future = this.future;
     future._asyncSetValue(value);
+    // The async-error will schedule another callback, so we can cancel
+    // the expectation without shutting down the zone.
+    future._zone.cancelCallbackExpectation();
   }
 
   void _setFutureError(error) {
     _FutureImpl future = this.future;
     future._asyncSetError(error);
+    // The async-error will schedule another callback, so we can cancel
+    // the expectation without shutting down the zone.
+    future._zone.cancelCallbackExpectation();
   }
 }
 
 class _SyncCompleter<T> extends _Completer<T> {
   void _setFutureValue(T value) {
     _FutureImpl future = this.future;
     future._setValue(value);
+    future._zone.cancelCallbackExpectation();
   }
 
   void _setFutureError(error) {
     _FutureImpl future = this.future;
     future._setError(error);
+    future._zone.cancelCallbackExpectation();
   }
 }
 
 /**
  * A listener on a future.
  *
  * When the future completes, the [_sendValue] or [_sendError] method
  * is invoked with the result.
  *
  * Listeners are kept in a linked list.
@@ skipping 596 matching lines @@
           _setError(error);
         }, onError: _setError);
         return;
       }
     } catch (e, s) {
       error = _asyncError(e, s);
     }
     _setError(error);
   }
 }