Fix Dialog and PopupMenu completion logic

packages/flutter/lib/src/material/dialog.dart

@@ -116,9 +116,8 @@ class Dialog extends StatelessComponent {
 }
 
 class _DialogRoute extends ModalRoute {
-  _DialogRoute({ this.completer, this.child });
+  _DialogRoute({ Completer completer, this.child }) : super(completer: completer);
 
-  final Completer completer;
   final Widget child;
 
   bool get opaque => false;
@@ -132,11 +131,6 @@ class _DialogRoute extends ModalRoute {
       child: child
     );
   }
-
-  void didPop([dynamic result]) {
-    completer.complete(result);
-    super.didPop(result);
-  }
 }
 
 Future showDialog({ BuildContext context, Widget child }) {

packages/flutter/lib/src/material/popup_menu.dart

@@ -93,9 +93,8 @@ class _PopupMenu extends StatelessComponent {
 }
 
 class _MenuRoute extends ModalRoute {
-  _MenuRoute({ this.completer, this.position, this.items, this.level });
+  _MenuRoute({ Completer completer, this.position, this.items, this.level }) : super(completer: completer);
 
-  final Completer completer;
   final ModalPosition position;
   final List<PopupMenuItem> items;
   final int level;
@@ -112,11 +111,6 @@ class _MenuRoute extends ModalRoute {
   Duration get transitionDuration => _kMenuDuration;
 
   Widget buildModalWidget(BuildContext context) => new _PopupMenu(route: this);
-
-  void didPop([dynamic result]) {
-    completer.complete(result);
-    super.didPop(result);
-  }
 }
 
 Future showMenu({ BuildContext context, ModalPosition position, List<PopupMenuItem> items, int level: 4 }) {

packages/flutter/lib/src/widgets/modal_barrier.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter/animation.dart';
 
 import 'basic.dart';
@@ -103,6 +105,8 @@ class ModalPosition {
 }
 
 abstract class ModalRoute extends TransitionRoute {
+  ModalRoute({ Completer completer }) : super(completer: completer);
+
   ModalPosition get position => null;
   Color get barrierColor => _kTransparent;
   Widget buildModalWidget(BuildContext context);

packages/flutter/lib/src/widgets/routes.dart

@@ -78,7 +78,8 @@ abstract class TransitionRoute extends OverlayRoute {
           overlayEntries.first.opaque = false;
         break;
       case PerformanceStatus.dismissed:
-        super.didPop(_result);
+        super.didPop(_result); // clear the overlays
+        completer?.complete(_result);
         break;
     }
   }
@@ -92,10 +93,7 @@ abstract class TransitionRoute extends OverlayRoute {
 
   void didPop(dynamic result) {
     _result = result;
-    if (completer != null)
-      _performance.reverse().then((_) { completer.complete(_result); });
-    else
-      _performance.reverse();
+    _performance.reverse();
   }
 
   String get debugLabel => '$runtimeType';

packages/unit/test/widget/snack_bar_test.dart

@@ -40,14 +40,20 @@ void main() {
         }
       ));
 
+      // TODO(hansmuller): find a way to avoid calling pump over and over.
+      // https://github.com/flutter/flutter/issues/348
+
       tester.tap(tester.findElementByKey(tapTarget));
       expect(tester.findText(helloSnackBar), isNull);
-      tester.pump();
+      tester.pump(new Duration(seconds: 1));
+      tester.pump(new Duration(seconds: 1));
       expect(tester.findText(helloSnackBar), isNotNull);
 
       Navigator.of(context).pop();
       expect(tester.findText(helloSnackBar), isNotNull);
       tester.pump(new Duration(seconds: 1));
+      tester.pump(new Duration(seconds: 1));
+      tester.pump(new Duration(seconds: 1));
       expect(showSnackBarThenCalled, isTrue);
       expect(tester.findText(helloSnackBar), isNull);
       expect(placeholderKey.currentState.child, isNull);