Rework error handling in the service protocol and in Observatory.

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

Index: runtime/observatory/lib/src/elements/instance_view.dart
diff --git a/runtime/observatory/lib/src/elements/instance_view.dart b/runtime/observatory/lib/src/elements/instance_view.dart
index 96598c78a5124e596f2c6bd93fab031db3cadd0d..14e69833475705cc20551e383e9accd080ff8e87 100644
--- a/runtime/observatory/lib/src/elements/instance_view.dart
+++ b/runtime/observatory/lib/src/elements/instance_view.dart
@@ -19,7 +19,7 @@ class InstanceViewElement extends ObservatoryElement {
     return instance.isolate.eval(instance, expression);
   }
 
-  void refresh(Function onDone) {
-    instance.reload().whenComplete(onDone);
+  Future refresh() {
+    return instance.reload();
   }
 }