Lazily format LanguageError messages (fix issue 15069).

runtime/vm/raw_object_snapshot.cc

Index: runtime/vm/raw_object_snapshot.cc
===================================================================
--- runtime/vm/raw_object_snapshot.cc	(revision 30304)
+++ runtime/vm/raw_object_snapshot.cc	(working copy)
@@ -1563,6 +1563,10 @@
   // Set the object tags.
   language_error.set_tags(tags);
 
+  // Set all non object fields.
+  language_error.set_token_pos(reader->ReadIntptrValue());
+  language_error.set_kind(reader->Read<uint8_t>());
+
   // Set all the object fields.
   // TODO(5411462): Need to assert No GC can happen here, even though
   // allocations may happen.
@@ -1590,6 +1594,10 @@
   writer->WriteVMIsolateObject(kLanguageErrorCid);
   writer->WriteIntptrValue(writer->GetObjectTags(this));
 
+  // Write out all the non object fields.
+  writer->WriteIntptrValue(ptr()->token_pos_);
+  writer->Write<uint8_t>(ptr()->kind_);
+
   // Write out all the object pointer fields.
   SnapshotWriterVisitor visitor(writer);
   visitor.VisitPointers(from(), to());