Refactor unboxed fields in preparation of reusable SIMD boxes

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index eaa5b725c250b0cdf4372e4b6e75a572ef437aab..eccf39fcdfcf2a37a690e0aa1511873a78c1edfe 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2187,17 +2187,14 @@ class Field : public Object {
     return r;
   }
 
-  bool IsUnboxedField() const {
-    return is_unboxing_candidate()
-        && !is_final()
-        && (guarded_cid() == kDoubleCid && !is_nullable());
+  intptr_t UnboxedFieldCid() const {
+    ASSERT(IsUnboxedField());
+    return guarded_cid();
   }
 
-  bool IsPotentialUnboxedField() const {
-    return is_unboxing_candidate()
-        && (IsUnboxedField() ||
-            (!is_final() && (guarded_cid() == kIllegalCid)));
-  }
+  bool IsUnboxedField() const;
+
+  bool IsPotentialUnboxedField() const;
 
   bool is_unboxing_candidate() const {
     return UnboxingCandidateBit::decode(raw_ptr()->kind_bits_);