Use PassiveObject were possible.

runtime/vm/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/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
@@ skipping 173 matching lines @@
       backward_references_((kind == Snapshot::kFull) ?
                            kNumInitialReferencesInFullSnapshot :
                            kNumInitialReferences) {
 }
 
 
 RawObject* SnapshotReader::ReadObject() {
   // Setup for long jump in case there is an exception while reading.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
-    Object& obj = Object::Handle(ReadObjectImpl());
+    PassiveObject& obj = PassiveObject::Handle(isolate(), ReadObjectImpl());
     for (intptr_t i = 0; i < backward_references_.length(); i++) {
       if (!backward_references_[i].is_deserialized()) {
         ReadObjectImpl();
         backward_references_[i].set_state(kIsDeserialized);
       }
     }
     return obj.raw();
   } else {
     // An error occurred while reading, return the error object.
     const Error& err = Error::Handle(isolate()->object_store()->sticky_error());
@@ skipping 1524 matching lines @@
     NoGCScope no_gc;
     WriteObject(obj.raw());
     UnmarkAll();
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart