Prevent flushing of code that was set with %SetCode.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 1b4ed5b3b572e8b7cb17b85bddf6479496ef692b..57084ed9f1f4a564b1c355b36dc591bbdc6de371 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6111,6 +6111,9 @@ class SharedFunctionInfo: public HeapObject {
   // Indicates that code for this function cannot be cached.
   DECL_BOOLEAN_ACCESSORS(dont_cache)
 
+  // Indicates that code for this function cannot be flushed.
+  DECL_BOOLEAN_ACCESSORS(dont_flush)
+
   // Indicates that this function is a generator.
   DECL_BOOLEAN_ACCESSORS(is_generator)
 
@@ -6340,6 +6343,7 @@ class SharedFunctionInfo: public HeapObject {
     kDontOptimize,
     kDontInline,
     kDontCache,
+    kDontFlush,
     kIsGenerator,
     kCompilerHintsCount  // Pseudo entry
   };