Add isolate tag-profile and better handling of errors

runtime/bin/vmservice/client/lib/src/service/service.dart

Index: runtime/bin/vmservice/client/lib/src/service/service.dart
diff --git a/runtime/bin/vmservice/client/lib/src/service/service.dart b/runtime/bin/vmservice/client/lib/src/service/service.dart
index 78c105dced1d6af9e80609a2492f3fc15e496fe3..8ee05019837d7ee3d31817ea0fc1cfe2ada1bc2b 100644
--- a/runtime/bin/vmservice/client/lib/src/service/service.dart
+++ b/runtime/bin/vmservice/client/lib/src/service/service.dart
@@ -44,20 +44,18 @@ void _upgradeObservableList(ObservableList list, VM vm, Isolate isolate) {
 /// This acts like a factory which consumes an ObservableMap and returns
 /// a fully upgraded ServiceObject.
 ServiceObject _upgradeToServiceObject(VM vm, Isolate isolate, ObservableMap m) {
-  if (m == null) {
-    return null;
-  }
-  if (!ServiceObject.isServiceMap(m)) {
-    Logger.root.severe("Malformed service object: $m");
-  }
   assert(ServiceObject.isServiceMap(m));
   var type = ServiceObject.stripRef(m['type']);
+  // ServiceError and ServiceExceptions are handled before we attempt
+  // to upgrade.
+  assert(type != 'ServiceError');
+  assert(type != 'ServiceException');
   switch (type) {
     case 'Error':
       if (isolate != null) {
-        return new ServiceError.fromMap(isolate, m);
+        return new DartError.fromMap(isolate, m);
       } else {
-        return new ServiceError.fromMap(vm, m);
+        return new DartError.fromMap(vm, m);
       }
       break;
     case 'Script':