Improve error message when attempting to evaluate against a VM-internal object (e.g., a Megamorphic…

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

Index: runtime/observatory/lib/src/elements/code_view.dart
diff --git a/runtime/observatory/lib/src/elements/code_view.dart b/runtime/observatory/lib/src/elements/code_view.dart
index 9234164b50a8693782d8a853cb2fce8d5e64fec6..d8fa1c77223b46a4b0bf38d5c5e5dc4379023178 100644
--- a/runtime/observatory/lib/src/elements/code_view.dart
+++ b/runtime/observatory/lib/src/elements/code_view.dart
@@ -210,7 +210,7 @@ class CodeViewElement extends ObservatoryElement {
       if (content is ServiceObject) {
         ServiceRefElement element = new Element.tag('any-service-ref');
         element.ref = content;
-        cell.append(element);
+        cell.children = [element];
       } else if (content != null) {
         cell.text = content.toString();
       }