[runtime] Make sure %ForInPrepare returns the correct length.

src/runtime/runtime-forin.cc

 // 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.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/factory.h"
 #include "src/isolate-inl.h"
 #include "src/objects-inl.h"
@@ skipping 13 matching lines @@
   Object* property_names = Runtime_GetPropertyNamesFast(
       1, Handle<Object>::cast(receiver).location(), isolate);
   if (isolate->has_pending_exception()) {
     return MakeTriple(property_names, nullptr, nullptr);
   }
 
   Handle<Object> cache_type(property_names, isolate);
   Handle<FixedArray> cache_array;
   int cache_length;
 
-  Handle<Map> receiver_map = handle(receiver->map(), isolate);
   if (cache_type->IsMap()) {
-    Handle<Map> cache_type_map =
-        handle(Handle<Map>::cast(cache_type)->map(), isolate);
-    DCHECK(cache_type_map.is_identical_to(isolate->factory()->meta_map()));
-    int enum_length = cache_type_map->EnumLength();
-    DescriptorArray* descriptors = receiver_map->instance_descriptors();
-    if (enum_length > 0 && descriptors->HasEnumCache()) {
+    Handle<Map> cache_type_map = Handle<Map>::cast(cache_type);
+    int const enum_length = cache_type_map->EnumLength();
+    DescriptorArray* descriptors = cache_type_map->instance_descriptors();
+    if (enum_length && descriptors->HasEnumCache()) {
       cache_array = handle(descriptors->GetEnumCache(), isolate);
-      cache_length = cache_array->length();
+      cache_length = enum_length;
     } else {
       cache_array = isolate->factory()->empty_fixed_array();
       cache_length = 0;
     }
   } else {
     cache_array = Handle<FixedArray>::cast(cache_type);
     cache_length = cache_array->length();
     // Cache type of SMI one entails slow check.
     cache_type = Handle<Object>(Smi::FromInt(1), isolate);
   }
@@ skipping 59 matching lines @@
   SealHandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_SMI_ARG_CHECKED(index, 0);
   DCHECK_LE(0, index);
   DCHECK_LT(index, Smi::kMaxValue);
   return Smi::FromInt(index + 1);
 }
 
 }  // namespace internal
 }  // namespace v8