AU: Topological Sort.

src/platform/update_engine/topological_sort.h

Index: src/platform/update_engine/topological_sort.h
diff --git a/src/platform/update_engine/topological_sort.h b/src/platform/update_engine/topological_sort.h
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+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_TOPOLOGICAL_SORT_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_TOPOLOGICAL_SORT_H__
+
+
+#include <vector>
+#include "update_engine/graph_types.h"
+
+namespace chromeos_update_engine {
+
+// Performs a topological sort on the directed graph 'graph' and stores
+// the nodes, in order visited, in 'out'.
+// For example, this graph:
+// A ---> C ----.
+//  \           v
+//   `--> B --> D
+// Might result in this in 'out':
+// out[0] = D
+// out[1] = B
+// out[2] = C
+// out[3] = A
+// Note: results are undefined if there is a cycle in the graph.
+void TopologicalSort(const Graph& graph, std::vector<Vertex::Index>* out);
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_TOPOLOGICAL_SORT_H__