Fix crash when setting breakpoint in Observatory

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 93ad49ce7a1d48d62baa1493e3ae2889d312a642..faeb61fbabb9ba609f7f020af7b9c4398855e151 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -3345,7 +3345,7 @@ void Class::set_token_pos(TokenPosition token_pos) const {
 
 TokenPosition Class::ComputeEndTokenPos() const {
   // Return the begin token for synthetic classes.
-  if (IsMixinApplication() || IsTopLevel()) {
+  if (is_synthesized_class() || IsMixinApplication() || IsTopLevel()) {
     return token_pos();
   }
   const Script& scr = Script::Handle(script());