Implement `in' for proxies.

src/objects.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1376 matching lines @@
   // Returns the constructor name (the name (possibly, inferred name) of the
   // function that was used to instantiate the object).
   String* constructor_name();
 
   inline PropertyAttributes GetPropertyAttribute(String* name);
   PropertyAttributes GetPropertyAttributeWithReceiver(JSReceiver* receiver,
                                                       String* name);
   PropertyAttributes GetLocalPropertyAttribute(String* name);
 
   // Can cause a GC.
-  bool HasProperty(String* name) {
-    return GetPropertyAttribute(name) != ABSENT;
-  }
-
-  // Can cause a GC.
-  bool HasLocalProperty(String* name) {
-    return GetLocalPropertyAttribute(name) != ABSENT;
-  }
+  inline bool HasProperty(String* name);
+  inline bool HasLocalProperty(String* name);
 
   // Return the object's prototype (might be Heap::null_value()).
   inline Object* GetPrototype();
 
   // Set the object's prototype (only JSReceiver and null are allowed).
   MUST_USE_RESULT MaybeObject* SetPrototype(Object* value,
                                             bool skip_hidden_prototypes);
 
   // Lookup a property.  If found, the result is valid and has
   // detailed information.
@@ skipping 5059 matching lines @@
  public:
   // [handler]: The handler property.
   DECL_ACCESSORS(handler, Object)
 
   // [padding]: The padding slot (unused, see below).
   DECL_ACCESSORS(padding, Object)
 
   // Casting.
   static inline JSProxy* cast(Object* obj);
 
+  bool HasPropertyWithHandler(String* name);
+
   MUST_USE_RESULT MaybeObject* SetPropertyWithHandler(
       String* name,
       Object* value,
       PropertyAttributes attributes,
       StrictModeFlag strict_mode);
 
   MUST_USE_RESULT MaybeObject* DeletePropertyWithHandler(
       String* name,
       DeleteMode mode);
 
@@ skipping 681 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_