Add GN split_list function

tools/gn/parse_node_value_adapter.cc

+// Copyright 2016 The Chromium 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 "tools/gn/parse_node_value_adapter.h"
+
+#include "tools/gn/parse_tree.h"
+#include "tools/gn/scope.h"
+
+ParseNodeValueAdapter::ParseNodeValueAdapter() : ref_(nullptr) {
+}
+
+ParseNodeValueAdapter::~ParseNodeValueAdapter() {
+}
+
+
+bool ParseNodeValueAdapter::Init(Scope* scope,
+                                 const ParseNode* node,
+                                 Err* err) {
+  const IdentifierNode* identifier = node->AsIdentifier();
+  if (identifier) {
+    ref_ = scope->GetValue(identifier->value().value(), true);
+    if (!ref_) {
+      identifier->MakeErrorDescribing("Undefined identifier");
+      return false;
+    }
+    return true;
+  }
+
+  temporary_ = node->Execute(scope, err);
+  return !err->has_error();
+}
+
+bool ParseNodeValueAdapter::InitForType(Scope* scope,
+                                        const ParseNode* node,
+                                        Value::Type type,
+                                        Err* err) {
+  if (!Init(scope, node, err))
+    return false;
+  if (get().VerifyTypeIs(type, err))
+    return true;
+
+  // Fix up the error range (see class comment in the header file) to be the
+  // identifier node rather than the original value.
+  *err = Err(node, err->message(), err->help_text());
+  return false;
+}