Fix snapshot generation to ensure that the snapshot does not contain

runtime/vm/raw_object_snapshot.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bigint_operations.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/snapshot.h"
 #include "vm/symbols.h"
 #include "vm/visitor.h"
@@ skipping 42 matching lines @@
       } else {
         cls = New<Instance>(kIllegalCid);
       }
     }
     reader->AddBackRef(object_id, &cls, kIsDeserialized);
 
     // Set the object tags.
     cls.set_tags(tags);
 
     // Set all non object fields.
-    cls.set_instance_size_in_words(reader->ReadIntptrValue());
+    if (!RawObject::IsInternalVMdefinedClassId(class_id)) {
+      // Instance size of a VM defined class is already set up.
+      cls.set_instance_size_in_words(reader->ReadIntptrValue());
+      cls.set_next_field_offset_in_words(reader->ReadIntptrValue());
+    }
     cls.set_type_arguments_field_offset_in_words(reader->ReadIntptrValue());
-    cls.set_next_field_offset_in_words(reader->ReadIntptrValue());
     cls.set_num_native_fields(reader->ReadIntptrValue());
     cls.set_token_pos(reader->ReadIntptrValue());
     cls.set_state_bits(reader->Read<uint16_t>());
 
     // Set all the object fields.
     // TODO(5411462): Need to assert No GC can happen here, even though
     // allocations may happen.
     intptr_t num_flds = (cls.raw()->to() - cls.raw()->from());
     for (intptr_t i = 0; i <= num_flds; i++) {
       *(cls.raw()->from() + i) = reader->ReadObjectRef();
@@ skipping 15 matching lines @@
 
   if ((kind == Snapshot::kFull) ||
       (kind == Snapshot::kScript &&
        !RawObject::IsCreatedFromSnapshot(writer->GetObjectTags(this)))) {
     // Write out the class and tags information.
     writer->WriteVMIsolateObject(kClassCid);
     writer->WriteIntptrValue(writer->GetObjectTags(this));
 
     // Write out all the non object pointer fields.
     // NOTE: cpp_vtable_ is not written.
-    writer->WriteIntptrValue(ptr()->id_);
-    writer->WriteIntptrValue(ptr()->instance_size_in_words_);
+    intptr_t class_id = ptr()->id_;
+    writer->WriteIntptrValue(class_id);
+    if (!RawObject::IsInternalVMdefinedClassId(class_id)) {
+      // We don't write the instance size of VM defined classes as they
+      // are already setup during initialization as part of pre populating
+      // the class table.
+      writer->WriteIntptrValue(ptr()->instance_size_in_words_);
+      writer->WriteIntptrValue(ptr()->next_field_offset_in_words_);
+    }
     writer->WriteIntptrValue(ptr()->type_arguments_field_offset_in_words_);
-    writer->WriteIntptrValue(ptr()->next_field_offset_in_words_);
     writer->WriteIntptrValue(ptr()->num_native_fields_);
     writer->WriteIntptrValue(ptr()->token_pos_);
     writer->Write<uint16_t>(ptr()->state_bits_);
 
     // Write out all the object pointer fields.
     SnapshotWriterVisitor visitor(writer);
     visitor.VisitPointers(from(), to());
   } else {
     writer->WriteClassId(this);
   }
@@ skipping 2523 matching lines @@
 }
 
 
 void RawMirrorReference::WriteTo(SnapshotWriter* writer,
                                  intptr_t object_id,
                                  Snapshot::Kind kind) {
   UNREACHABLE();
 }
 
 }  // namespace dart