V8 support for cached accessors.

src/lookup.h

Index: src/lookup.h
diff --git a/src/lookup.h b/src/lookup.h
index 2028427cf62473302417b168d6b08f8f04c10e79..4e2c69f1e6d499df15bbec35c17ba4ba3129a120 100644
--- a/src/lookup.h
+++ b/src/lookup.h
@@ -263,6 +263,11 @@ class V8_EXPORT_PRIVATE LookupIterator final BASE_EMBEDDED {
     }
   }
 
+  // Lookup a 'cached' private property for an accessor.
+  // If not found returns false and leaves the LookupIterator unmodified.
+  bool TryLookupCachedProperty();
+  bool LookupCachedProperty();
+
  private:
   void InternalUpdateProtector();