Create a internal, global native context used only for generated code stubs

src/snapshot/serialize.h

Index: src/snapshot/serialize.h
diff --git a/src/snapshot/serialize.h b/src/snapshot/serialize.h
index 001d7753922915989cb059888ed11579db4c5c8f..245cc7746dd50e18ca9ed69f84a5985ce32494a2 100644
--- a/src/snapshot/serialize.h
+++ b/src/snapshot/serialize.h
@@ -396,8 +396,11 @@ class SerializerDeserializer: public ObjectVisitor {
   static const int kVariableRepeat = 0x77;
   // Alignment prefixes 0x7d..0x7f
   static const int kAlignmentPrefix = 0x7d;
+  // Used for the source code for compiled stubs, which is in the executable,
+  // but is referred to from external strings in the snapshot.
+  static const int kCodeStubNativesStringResource = 0x5d;
 
-  // 0x5d..0x5f unused
+  // 0x5e..0x5f unused
 
   // ---------- byte code range 0x80..0xff ----------
   // First 32 root array items.