[objects.h splitting] Move out ConstantElementsPair and BoileplateDescriptor.

src/objects/literal-objects.cc

+// Copyright 2017 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/objects/literal-objects.h"
+
+#include "src/factory.h"
+#include "src/isolate.h"
+#include "src/objects-inl.h"
+
+namespace v8 {
+namespace internal {
+
+Object* BoilerplateDescription::name(int index) const {
+  // get() already checks for out of bounds access, but we do not want to allow
+  // access to the last element, if it is the number of properties.
+  DCHECK_NE(size(), index);
+  return get(2 * index);
+}
+
+Object* BoilerplateDescription::value(int index) const {
+  return get(2 * index + 1);
+}
+
+int BoilerplateDescription::size() const {
+  DCHECK_EQ(0, (length() - (this->has_number_of_properties() ? 1 : 0)) % 2);
+  // Rounding is intended.
+  return length() / 2;
+}
+
+int BoilerplateDescription::backing_store_size() const {
+  if (has_number_of_properties()) {
+    // If present, the last entry contains the number of properties.
+    return Smi::cast(this->get(length() - 1))->value();
+  }
+  // If the number is not given explicitly, we assume there are no
+  // properties with computed names.
+  return size();
+}
+
+void BoilerplateDescription::set_backing_store_size(Isolate* isolate,
+                                                    int backing_store_size) {
+  DCHECK(has_number_of_properties());
+  DCHECK_NE(size(), backing_store_size);
+  Handle<Object> backing_store_size_obj =
+      isolate->factory()->NewNumberFromInt(backing_store_size);
+  set(length() - 1, *backing_store_size_obj);
+}
+
+bool BoilerplateDescription::has_number_of_properties() const {
+  return length() % 2 != 0;
+}
+
+}  // namespace internal
+}  // namespace v8