Add debug checks to catch PropertyCell::cast failures.

src/lookup.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/lookup.h"
 #include "src/lookup-inl.h"
@@ skipping 238 matching lines @@
   return false;
 }
 
 
 Handle<Object> LookupIterator::FetchValue() const {
   Object* result = NULL;
   Handle<JSObject> holder = GetHolder<JSObject>();
   if (holder_map_->is_dictionary_map()) {
     result = holder->property_dictionary()->ValueAt(number_);
     if (holder_map_->IsGlobalObjectMap()) {
+      DCHECK(result->IsPropertyCell());
       result = PropertyCell::cast(result)->value();
     }
   } else if (property_details_.type() == v8::internal::DATA) {
     FieldIndex field_index = FieldIndex::ForDescriptor(*holder_map_, number_);
     return JSObject::FastPropertyAt(holder, property_details_.representation(),
                                     field_index);
   } else {
     result = holder_map_->instance_descriptors()->GetValue(number_);
   }
   return handle(result, isolate_);
@@ skipping 34 matching lines @@
   return handle(
       holder_map_->instance_descriptors()->GetFieldType(descriptor_number()),
       isolate_);
 }
 
 
 Handle<PropertyCell> LookupIterator::GetPropertyCell() const {
   Handle<JSObject> holder = GetHolder<JSObject>();
   Handle<GlobalObject> global = Handle<GlobalObject>::cast(holder);
   Object* value = global->property_dictionary()->ValueAt(dictionary_entry());
+  DCHECK(value->IsPropertyCell());
   return Handle<PropertyCell>(PropertyCell::cast(value));
 }
 
 
 Handle<Object> LookupIterator::GetAccessors() const {
   DCHECK_EQ(ACCESSOR, state_);
   return FetchValue();
 }
 
 
@@ skipping 61 matching lines @@
       // Fall through.
       case InterceptorState::kSkipNonMasking:
         return true;
       case InterceptorState::kProcessNonMasking:
         return false;
     }
   }
   return interceptor_state_ == InterceptorState::kProcessNonMasking;
 }
 } }  // namespace v8::internal