add interceptors which do not mask existing properties

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index c3344ec98759a28b767e29f5ba440065f210fe21..d9f30310c06f71d0c985887e052416f9314fe947 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -10569,6 +10569,7 @@ class InterceptorInfo: public Struct {
   DECL_ACCESSORS(data, Object)
   DECL_BOOLEAN_ACCESSORS(can_intercept_symbols)
   DECL_BOOLEAN_ACCESSORS(all_can_read)
+  DECL_BOOLEAN_ACCESSORS(non_masking)
 
   inline int flags() const;
   inline void set_flags(int flags);
@@ -10590,6 +10591,7 @@ class InterceptorInfo: public Struct {
 
   static const int kCanInterceptSymbolsBit = 0;
   static const int kAllCanReadBit = 1;
+  static const int kNonMasking = 2;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(InterceptorInfo);