Make JSProxies always be in slow mode

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 2abfb9dd816e7325d3f76594fd5561cf9f98fcbf..3330783e3a0fdba74a6e1c5569dbced587152597 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3219,6 +3219,9 @@ class HashTable : public HashTableBase {
       Key key,
       PretenureFlag pretenure = NOT_TENURED);
 
+  // Returns true if this table has sufficient capacity for adding n elements.
+  bool HasSufficientCapacity(int n);
+
   // Sets the capacity of the hash table.
   void SetCapacity(int capacity) {
     // To scale a computed hash code to fit within the hash table, we
@@ -3418,6 +3421,9 @@ class Dictionary: public HashTable<Derived, Shape, Key> {
       int at_least_space_for,
       PretenureFlag pretenure = NOT_TENURED);
 
+  // Ensures that a new dictionary is created when the capacity is checked.
+  void SetRequiresCopyOnCapacityChange();
+
   // Ensure enough space for n additional elements.
   static Handle<Derived> EnsureCapacity(Handle<Derived> obj, int n, Key key);