Add initial prototype for the GN meta-buildsystem.

tools/gn/item_node.cc

Index: tools/gn/item_node.cc
diff --git a/tools/gn/item_node.cc b/tools/gn/item_node.cc
new file mode 100644
index 0000000000000000000000000000000000000000..776a126b19036b73cd32651aa44c34357832b872
--- /dev/null
+++ b/tools/gn/item_node.cc
@@ -0,0 +1,51 @@
+// Copyright (c) 2013 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/item_node.h"
+
+#include <algorithm>
+
+#include "base/callback.h"
+#include "base/logging.h"
+#include "tools/gn/item.h"
+
+ItemNode::ItemNode(Item* i)
+    : state_(REFERENCED),
+      item_(i) {
+}
+
+ItemNode::~ItemNode() {
+}
+
+void ItemNode::AddDependency(ItemNode* node) {
+  if (direct_dependencies_.find(node) != direct_dependencies_.end())
+    return;  // Already have this dep.
+  direct_dependencies_.insert(node);
+
+  if (node->state() != RESOLVED) {
+    // Wire up the pending resolution info.
+    unresolved_dependencies_.insert(node);
+    node->waiting_on_resolution_.insert(this);
+  }
+}
+
+void ItemNode::MarkDirectDependencyResolved(ItemNode* node) {
+  DCHECK(unresolved_dependencies_.find(node) != unresolved_dependencies_.end());
+  unresolved_dependencies_.erase(node);
+}
+
+void ItemNode::SwapOutWaitingDependencySet(ItemNodeSet* out_set) {
+  waiting_on_resolution_.swap(*out_set);
+}
+
+void ItemNode::SetGenerated() {
+  state_ = GENERATED;
+}
+
+void ItemNode::SetResolved() {
+  state_ = RESOLVED;
+
+  if (!resolved_closure_.is_null())
+    resolved_closure_.Run();
+}