Rely on the map being a dictionary map rather than not having a backpointer

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 218 matching lines @@
   state_ = TRANSITION;
   transition_ = transition;
 
   if (receiver->IsGlobalObject()) {
     // Install a property cell.
     InternalizeName();
     auto cell = GlobalObject::EnsurePropertyCell(
         Handle<GlobalObject>::cast(receiver), name());
     DCHECK(cell->value()->IsTheHole());
     transition_ = cell;
-  } else if (transition->GetBackPointer()->IsMap()) {
+  } else if (!transition->is_dictionary_map()) {
     property_details_ = transition->GetLastDescriptorDetails();
     has_property_ = true;
   }
 }
 
 
 void LookupIterator::ApplyTransitionToDataProperty() {
   DCHECK_EQ(TRANSITION, state_);
 
   Handle<JSObject> receiver = GetStoreTarget();
@@ skipping 253 matching lines @@
       case InterceptorState::kSkipNonMasking:
         return true;
       case InterceptorState::kProcessNonMasking:
         return false;
     }
   }
   return interceptor_state_ == InterceptorState::kProcessNonMasking;
 }
 }  // namespace internal
 }  // namespace v8