Speed up PrototypeHasNoElements and drop the "fast" path before, it's now slower.

src/objects.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/assert-scope.h"
@@ skipping 691 matching lines @@
 
   // All the following types are subtypes of JSReceiver, which corresponds to
   // objects in the JS sense. The first and the last type in this range are
   // the two forms of function. This organization enables using the same
   // compares for checking the JS_RECEIVER and the NONCALLABLE_JS_OBJECT range.
   JS_PROXY_TYPE,          // FIRST_JS_RECEIVER_TYPE
   JS_GLOBAL_OBJECT_TYPE,  // FIRST_JS_OBJECT_TYPE
   JS_GLOBAL_PROXY_TYPE,
   // Like JS_OBJECT_TYPE, but requires access checks and/or has interceptors.
   JS_SPECIAL_API_OBJECT_TYPE,  // LAST_SPECIAL_RECEIVER_TYPE
-  JS_VALUE_TYPE,
+  JS_VALUE_TYPE,               // LAST_CUSTOM_ELEMENTS_RECEIVER
   JS_MESSAGE_OBJECT_TYPE,
   JS_DATE_TYPE,
   JS_OBJECT_TYPE,
   JS_CONTEXT_EXTENSION_OBJECT_TYPE,
   JS_GENERATOR_OBJECT_TYPE,
   JS_MODULE_TYPE,
   JS_ARRAY_TYPE,
   JS_ARRAY_BUFFER_TYPE,
   JS_TYPED_ARRAY_TYPE,
   JS_DATA_VIEW_TYPE,
@@ skipping 30 matching lines @@
   // are not continuous in this enum! The enum ranges instead reflect the
   // external class names, where proxies are treated as either ordinary objects,
   // or functions.
   FIRST_JS_RECEIVER_TYPE = JS_PROXY_TYPE,
   LAST_JS_RECEIVER_TYPE = LAST_TYPE,
   // Boundaries for testing the types represented as JSObject
   FIRST_JS_OBJECT_TYPE = JS_GLOBAL_OBJECT_TYPE,
   LAST_JS_OBJECT_TYPE = LAST_TYPE,
   // Boundary for testing JSReceivers that need special property lookup handling
   LAST_SPECIAL_RECEIVER_TYPE = JS_SPECIAL_API_OBJECT_TYPE,
+  // Boundary case for testing JSReceivers that may have elements while having
+  // an empty fixed array as elements backing store. This is true for string
+  // wrappers.
+  LAST_CUSTOM_ELEMENTS_RECEIVER = JS_VALUE_TYPE,
 };
 
 STATIC_ASSERT(JS_OBJECT_TYPE == Internals::kJSObjectType);
 STATIC_ASSERT(FIRST_NONSTRING_TYPE == Internals::kFirstNonstringType);
 STATIC_ASSERT(ODDBALL_TYPE == Internals::kOddballType);
 STATIC_ASSERT(FOREIGN_TYPE == Internals::kForeignType);
 
 
 std::ostream& operator<<(std::ostream& os, InstanceType instance_type);
 
@@ skipping 10119 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_