Don't use ConsStringIterator to compute string hashes

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 96e044596d29a67bc71aa4c746a44b0c2180f1ac..0bdbd84bc583a1bd4bb4c39efdd6803ece083ba0 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -962,6 +962,8 @@ class Isolate {
     return &regexp_macro_assembler_canonicalize_;
   }
 
+  uint16_t* cons_string_hashing_buffer() { return cons_string_hashing_buffer_; }
+
   RegExpStack* regexp_stack() { return regexp_stack_; }
 
   unibrow::Mapping<unibrow::Ecma262Canonicalize>*
@@ -1264,6 +1266,7 @@ class Isolate {
   unibrow::Mapping<unibrow::CanonicalizationRange> jsregexp_canonrange_;
   unibrow::Mapping<unibrow::Ecma262Canonicalize>
       regexp_macro_assembler_canonicalize_;
+  uint16_t* cons_string_hashing_buffer_;
   RegExpStack* regexp_stack_;
   DateCache* date_cache_;
   unibrow::Mapping<unibrow::Ecma262Canonicalize> interp_canonicalize_mapping_;