Add debug checks to catch PropertyCell::cast failures.

src/lookup-inl.h

 // Copyright 2014 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_LOOKUP_INL_H_
 #define V8_LOOKUP_INL_H_
 
 #include "src/lookup.h"
 
 namespace v8 {
@@ skipping 44 matching lines @@
           !SkipInterceptor(JSObject::cast(holder))) {
         return INTERCEPTOR;
       }
     // Fall through.
     case INTERCEPTOR:
       if (map->is_dictionary_map()) {
         NameDictionary* dict = JSObject::cast(holder)->property_dictionary();
         number_ = dict->FindEntry(name_);
         if (number_ == NameDictionary::kNotFound) return NOT_FOUND;
         if (holder->IsGlobalObject()) {
+          DCHECK(dict->ValueAt(number_)->IsPropertyCell());
           PropertyCell* cell = PropertyCell::cast(dict->ValueAt(number_));
           if (cell->value()->IsTheHole()) return NOT_FOUND;
         }
         property_details_ = dict->DetailsAt(number_);
       } else {
         DescriptorArray* descriptors = map->instance_descriptors();
         number_ = descriptors->SearchWithCache(*name_, map);
         if (number_ == DescriptorArray::kNotFound) return NOT_FOUND;
         property_details_ = descriptors->GetDetails(number_);
       }
@@ skipping 29 matching lines @@
     default:
       return NOT_FOUND;
   }
   UNREACHABLE();
   return state_;
 }
 }
 }  // namespace v8::internal
 
 #endif  // V8_LOOKUP_INL_H_