[turbofan] Add support for SOFT deopts and use that for property access.

src/type-feedback-vector.h

Index: src/type-feedback-vector.h
diff --git a/src/type-feedback-vector.h b/src/type-feedback-vector.h
index d83b77fa3e6f8e628f67f864f74291daf676066f..d1c31a285fb656162ddcc6043d2ce89bebc4c17d 100644
--- a/src/type-feedback-vector.h
+++ b/src/type-feedback-vector.h
@@ -343,6 +343,7 @@ class FeedbackNexus {
   FeedbackVectorSlot slot() const { return slot_; }
 
   InlineCacheState ic_state() const { return StateFromFeedback(); }
+  bool IsUninitialized() const { return StateFromFeedback() == UNINITIALIZED; }
   Map* FindFirstMap() const {
     MapHandleList maps;
     ExtractMaps(&maps);