Split GuardField into GuardFieldType and GuardFieldLength instructions.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index 74de207d89bcdeb6c8a034cd85ae4d17f6d75034..c8deea97b14c3dde4bb4a2e1686df94a8dfdd51e 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -858,7 +858,7 @@ RawObject* SnapshotReader::ReadInlinedObject(intptr_t object_id) {
         field_ ^= array_.At(offset >> kWordSizeLog2);
         ASSERT(!field_.IsNull());
         ASSERT(field_.Offset() == offset);
-        field_.UpdateGuardedCidAndLength(obj_);
+        field_.RecordStore(obj_);
       }
       // TODO(fschneider): Verify the guarded cid and length for other kinds of
       // snapshot (kFull, kScript) with asserts.