Serializer: ensure unique script ids when deserializing.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 5c276e9581c5fa2aac11a33db53cd7dd96a444b5..8e4952e8a83fb5e2d577a42f50eef38af99c16e9 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1349,6 +1349,14 @@ class Heap {
     return seed;
   }
 
+  Smi* NextScriptId() {
+    int next_id = last_script_id()->value() + 1;
+    if (!Smi::IsValid(next_id) || next_id < 0) next_id = 1;
+    Smi* next_id_smi = Smi::FromInt(next_id);
+    set_last_script_id(next_id_smi);
+    return next_id_smi;
+  }
+
   void SetArgumentsAdaptorDeoptPCOffset(int pc_offset) {
     DCHECK(arguments_adaptor_deopt_pc_offset() == Smi::FromInt(0));
     set_arguments_adaptor_deopt_pc_offset(Smi::FromInt(pc_offset));