[turbofan] Treat PREMONOMORPHIC like UNINITIALIZED.

src/type-feedback-vector.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_TYPE_FEEDBACK_VECTOR_H_
 #define V8_TYPE_FEEDBACK_VECTOR_H_
 
 #include <vector>
 
 #include "src/base/logging.h"
@@ skipping 382 matching lines @@
     DCHECK(vector_ == NULL);
     return vector_handle_;
   }
   TypeFeedbackVector* vector() const {
     return vector_handle_.is_null() ? vector_ : *vector_handle_;
   }
   FeedbackVectorSlot slot() const { return slot_; }
 
   InlineCacheState ic_state() const { return StateFromFeedback(); }
   bool IsUninitialized() const { return StateFromFeedback() == UNINITIALIZED; }
+  bool IsPremonomorphic() const {
+    return StateFromFeedback() == PREMONOMORPHIC;
+  }
   Map* FindFirstMap() const {
     MapHandleList maps;
     ExtractMaps(&maps);
     if (maps.length() > 0) return *maps.at(0);
     return NULL;
   }
 
   // TODO(mvstanton): remove FindAllMaps, it didn't survive a code review.
   void FindAllMaps(MapHandleList* maps) const { ExtractMaps(maps); }
 
@@ skipping 214 matching lines @@
   KeyedAccessStoreMode GetKeyedAccessStoreMode() const;
   IcCheckType GetKeyType() const;
 
   InlineCacheState StateFromFeedback() const override;
   Name* FindFirstName() const override;
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TRANSITIONS_H_