Add initial prototype for the GN meta-buildsystem.

tools/gn/config_values_extractors.h

Index: tools/gn/config_values_extractors.h
diff --git a/tools/gn/config_values_extractors.h b/tools/gn/config_values_extractors.h
new file mode 100644
index 0000000000000000000000000000000000000000..0eaa2c9263b61509e7f595384700866a8bcab655
--- /dev/null
+++ b/tools/gn/config_values_extractors.h
@@ -0,0 +1,50 @@
+// 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.
+
+#ifndef TOOLS_GN_CONFIG_VALUES_EXTRACTORS_H_
+#define TOOLS_GN_CONFIG_VALUES_EXTRACTORS_H_
+
+#include <ostream>
+#include <string>
+#include <vector>
+
+#include "tools/gn/config.h"
+#include "tools/gn/config_values.h"
+#include "tools/gn/target.h"
+
+template<typename T, class Writer>
+inline void ConfigValuesToStream(
+    const ConfigValues& values,
+    const std::vector<T>& (ConfigValues::* getter)() const,
+    const Writer& writer,
+    std::ostream& out) {
+  const std::vector<T>& v = (values.*getter)();
+  for (size_t i = 0; i < v.size(); i++)
+    writer(v[i], out);
+};
+
+template<typename T, class Writer>
+inline void RecursiveTargetConfigToStream(
+    const Target* target,
+    const std::vector<T>& (ConfigValues::* getter)() const,
+    const Writer& writer,
+    std::ostream& out) {
+  // Write all configs in reverse order (to get oldest first, which will look
+  // more normal in the output).
+  for (int i = static_cast<int>(target->configs().size() - 1); i >= 0; i--) {
+    ConfigValuesToStream(target->configs()[i]->config_values(), getter,
+                         writer, out);
+  }
+
+  // Last write from the config from the Target itself, if any.
+  ConfigValuesToStream(target->config_values(), getter, writer, out);
+}
+
+// Writes the values out as strings with no transformation.
+void RecursiveTargetConfigStringsToStream(
+    const Target* target,
+    const std::vector<std::string>& (ConfigValues::* getter)() const,
+    std::ostream& out);
+
+#endif  // TOOLS_GN_CONFIG_VALUES_EXTRACTORS_H_