Introduce FieldIndex to unify and abstract property/field offset

src/field-index.cc

+// 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.
+
+#include "src/v8.h"
+
+#include "src/field-index.h"
+#include "src/objects.h"
+#include "src/objects-inl.h"
+
+namespace v8 {
+namespace internal {
+
+
+FieldIndex FieldIndex::ForLookupResult(const LookupResult* lookup_result) {
+  Map* map = lookup_result->holder()->map();
+  return ForPropertyIndex(map,
+                          lookup_result->GetFieldIndexFromMap(map),
+                          lookup_result->representation().IsDouble());
+}
+
+
+} }  // namespace v8::internal