Rework error handling in the service protocol and in Observatory.

runtime/observatory/lib/src/elements/vm_view.dart

Index: runtime/observatory/lib/src/elements/vm_view.dart
diff --git a/runtime/observatory/lib/src/elements/vm_view.dart b/runtime/observatory/lib/src/elements/vm_view.dart
index 23977050108f2f59a4a56b9c19a7a6265dd4c43d..6f825626ccc165461d199a616813325029c90ff0 100644
--- a/runtime/observatory/lib/src/elements/vm_view.dart
+++ b/runtime/observatory/lib/src/elements/vm_view.dart
@@ -4,6 +4,7 @@
 
 library vm_view_element;
 
+import 'dart:async';
 import 'observatory_element.dart';
 import 'package:observatory/service.dart';
 import 'package:polymer/polymer.dart';
@@ -15,7 +16,7 @@ class VMViewElement extends ObservatoryElement {
 
   VMViewElement.created() : super.created();
 
-  void refresh(var done) {
-    vm.reload().then((vm) => vm.reloadIsolates()).whenComplete(done);
+  Future refresh() {
+    return vm.reload().then((vm) => vm.reloadIsolates());
   }
 }