[serializer] do not cache resource data pointer for native source.

src/snapshot/serializer.cc

Index: src/snapshot/serializer.cc
diff --git a/src/snapshot/serializer.cc b/src/snapshot/serializer.cc
index f6f2200775be526712a44cc762b88983bfb37a42..1fbef5ed89eee196bf7aae93168cb4de3fcef3c8 100644
--- a/src/snapshot/serializer.cc
+++ b/src/snapshot/serializer.cc
@@ -687,6 +687,9 @@ bool Serializer::ObjectSerializer::SerializeExternalNativeSourceString(
 
 void Serializer::ObjectSerializer::VisitExternalOneByteString(
     v8::String::ExternalOneByteStringResource** resource_pointer) {
+  DCHECK_EQ(serializer_->isolate()->heap()->native_source_string_map(),
+            object_->map());
+  DCHECK(ExternalOneByteString::cast(object_)->is_short());
   Address references_start = reinterpret_cast<Address>(resource_pointer);
   OutputRawData(references_start);
   if (SerializeExternalNativeSourceString(