VM: Field::IsConsistentWith should check unboxing state of the field.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 2230804961db36e47b5ee0f7c862502dc89fdcb2..de74eb4dd2133ee8af70c1bb79a929d7238962bb 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -7709,7 +7709,8 @@ bool Field::IsConsistentWith(const Field& other) const {
   return (raw_ptr()->guarded_cid_ == other.raw_ptr()->guarded_cid_) &&
          (raw_ptr()->is_nullable_ == other.raw_ptr()->is_nullable_) &&
          (raw_ptr()->guarded_list_length_ ==
-             other.raw_ptr()->guarded_list_length_);
+             other.raw_ptr()->guarded_list_length_) &&
+         (is_unboxing_candidate() == other.is_unboxing_candidate());
 }