Special handling for inline caches in code serializer.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index af6bb667e16863aefb33957aa22710afc5c5234d..d944bee72a1082a2695b8263f2e11a6d46691047 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -5150,6 +5150,10 @@ class Code: public HeapObject {
   inline void set_profiler_ticks(int ticks);
 
   // [builtin_index]: For BUILTIN kind, tells which builtin index it has.
+  // For builtins, tells which builtin index it has.
+  // Note that builtins can have a code kind other than BUILTIN, which means
+  // that for arbitrary code objects, this index value may be random garbage.
+  // To verify in that case, compare the code object to the indexed builtin.
   inline int builtin_index();
   inline void set_builtin_index(int id);