Merge pull request #1110 from abarth/widgets_back

Move default back behavior to FlutterWidgetBinding

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

@@ -86,11 +86,11 @@ class _MaterialAppState extends State<MaterialApp> implements BindingObserver {
     assert(mounted);
     NavigatorState navigator = _navigator.currentState;
     assert(navigator != null);
+    bool result = false;
     navigator.openTransaction((NavigatorTransaction transaction) {
-      if (!transaction.pop())
-        activity.finishCurrentActivity();
+      result = transaction.pop();
     });
-    return true;
+    return result;
   }
 
   void didChangeSize(Size size) => setState(() { _size = size; });

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

@@ -77,8 +77,9 @@ class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, Rendere
   void handlePopRoute() {
     for (BindingObserver observer in _observers) {
       if (observer.didPopRoute())
-        break;
+        return;
     }
+    activity.finishCurrentActivity();
   }
 
   void handleAppLifecycleStateChanged(ui.AppLifecycleState state) {